Biomedical subjects

William L Farrar

Publications and source records attributed to William L Farrar.

At least 19 recordsLinked to original sources

PubMed2007

TGFBR3 loss and consequences in prostate cancer.

BACKGROUND: Resistance to transforming growth factor-beta (TGF-beta) is important in tumorigenesis. TGF-beta resistance mechanisms in prostate cancer are not well understood. METHODS: We have conducted a systematic analysis of TGF-beta pathway components with a meta-analysis of seven microarray studies using Oncomine and evaluated the results of TGFBR3 expression in prostate cell lines. Furthermore, we knocked down TGFBR3 in prostate epithelial cells and analyzed the consequences of TGFBR3 knockdown. RESULTS: We found that TGFBR3 is the TGF-beta component most commonly downregulated among localized human prostate cancer studies. TGFBR3 knockdown led to focus formation and enhanced expression of CD133, a marker found on prostate cancer stem cells. DNA microarray analysis of TGFBR3 knockdown cells identified 101 genes regulated by TGFBR3. Seven of these genes show a corresponding decrease in clinical prostate cancer specimens, which include genes involved in prostate mass and vasculature. CONCLUSIONS: TGFBR3 downregulation is an important step in prostate tumorigenesis.

Blotting, Western↗

PubMed2006

Integrated molecular profiling of SOD2 expression in multiple myeloma.

Reactive oxygen species are known to be involved in several cellular processes, including cell signaling. SOD2 is a key enzyme in the conversion of reactive oxygen species and has been implicated in a host of disease states, including cancer. Using an integrated, whole-cell approach encompassing epigenetics, genomics, and proteomics, we have defined the role of SOD2 in multiple myeloma. We show that the SOD2 promoter is methylated in several cell lines and there is a correlative decrease in expression. Furthermore, myeloma patient samples have decreased SOD2 expression compared with healthy donors. Overexpression of SOD2 results in decreased proliferation and altered sensitivity to 2-methoxyestradiol-induced DNA damage and apoptosis. Genomic profiling revealed regulation of 65 genes, including genes involved in tumorigenesis, and proteomic analysis identified activation of the JAK/STAT pathway. Analysis of nearly 400 activated transcription factors identified 31 transcription factors with altered DNA binding activity, including XBP1, NFAT, forkhead, and GAS binding sites. Integration of data from our gestalt molecular analysis has defined a role for SOD2 in cellular proliferation, JAK/STAT signaling, and regulation of several transcription factors.

2-Methoxyestradiol↗

PubMed2006

Reversal of p53 epigenetic silencing in multiple myeloma permits apoptosis by a p53 activator.

Inactivation of the p53 pathway is a common feature of neoplasia. Dysregulation of the p53 pathway has been shown to involve mutations of p53, increased expression of the p53 inhibitor HDM-2, or epigenetic silencing of the p53 promoter. In multiple myeloma, a neoplasia of terminally differentiated B cells, p53 mutations and deletions are relatively rare and occur in late stage disease. Here, we show that the p53 promoter is hypermethylated in several multiple myeloma cell lines in comparison to normal plasma cells. Two cell lines containing mutant p53, Lp-1 and OPM-2, show a methylation pattern that suggests that they contain one methylated and one unmethylated mutant allele. Two other cell lines, KMS-11 and OPM-2, show hypermethylation of p53 with a lack of expression. In all cell lines tested, treatment with a demethylating agents results in higher expression of p53. Furthermore, following increased expression of p53, treatment of the myeloma cell lines with a p53 activating peptide induces apoptosis. Therefore, combinatorial treatment with demethylating agents followed by delivery of a p53 activating peptide may be an effective therapeutic strategy against multiple myeloma.

Amino Acid Sequence↗

PubMed2006

Stem cells in prostate cancer: resolving the castrate-resistant conundrum and implications for hormonal therapy.

Androgen deprivation therapy (ADT) is initial systemic therapy for advanced prostate cancer and is used as an adjuvant to local therapy for high-risk disease, but responses in advanced disease are transient. Prostate cancer stem cells are a small fraction of tumor cells that give rise to malignant cells. Initial or acquired stem cell resistance to castration must therefore underlie castrate-resistant prostate cancer. We sought to review the evidence on cancer stem cells and androgen deprivation therapy to determine if prostate cancer stem cell resistance occurs from the outset, or if it is an acquired resistance. Prostate cancer stem cells do not express androgen receptor (AR) and hence should not be directly responsive to androgen deprivation therapy. However, castrate-resistant tumors that are derived from stem cells, have molecular changes such as amplification of the androgen receptor gene, or other genetic changes resulting in gain-of-function changes in AR, implying an acquired resistance to androgen deprivation. The origins of castrate-resistant tumors, with mechanisms such as androgen receptor gene amplification from androgen receptor negative prostate cancer stem cells, is an apparent conundrum. Insight into how this occurs may lead to new treatments that overcome or delay castrate-resistance. Herein, we review the evidence on cancer stem cells, the benefits of ADT, the biological basis of response to ADT, and mechanisms of castrate-resistance. We also explore the apparent conundrum of why AR-negative prostate cancer stem cells can give rise to castrate-resistant prostate cancer. We propose possible explanations that may resolve this conundrum and discuss implications for hormonal therapy.

Androgen Antagonists↗

PubMed2006

Disruption of estrogen receptor DNA-binding domain and related intramolecular communication restores tamoxifen sensitivity in resistant breast cancer.

A serious obstacle to successful treatment of estrogen receptor (ER)-positive human breast cancer is cell resistance to tamoxifen (TAM) therapy. Here we show that the electrophile disulfide benzamide (DIBA), an ER zinc finger inhibitor, blocks ligand-dependent and -independent cell growth of TAM-resistant breast cancer in vitro and in vivo. Such inhibition depends on targeting disruption of the ER DNA-binding domain and its communication with neighboring functional domains, facilitating ERalpha dissociation from its coactivator AIB1 and concomitant association with its corepressor NCoR bound to chromatin. DIBA does not affect phosphorylation of HER2, MAPK, AKT, and AIB1, suggesting that DIBA-modified ERalpha may induce a switch from agonistic to antagonistic effects of TAM on resistant breast cancer cells.

Animals↗

PubMed2005

Perturbations in hypoxia detection: a shared link between hereditary and sporadic tumor formation?

The discovery and characterization of the von Hippel Lindau (VHL) syndrome has brought about tremendous advances in understanding the molecular mechanisms of renal cell carcinoma. VHL mutations are known to act through hypoxia inducible factor, which has a physiologic role in detecting hypoxia. Recent investigations into other hereditary forms of kidney cancer with mutations in genes involving energy metabolism and oxidative changes, such as fumarate hydratase, suggest that metabolic changes related to hypoxia detection may be a common mechanism of tumorigenesis. This implicates aberrations in the kidney's physiologic role in detection of hypoxia in tumor formation. Germline mutations of genes involved in energy metabolism and oxidative perturbations lead to tumors in other tissues that detect hypoxia, such as head and neck paragangliomas that occur in the area of the carotid body. Therefore, aberrations in physiologic detection of hypoxia that predispose to tumor formation may not be a mechanism unique to the kidney. Furthermore, inducers of hypoxic perturbations other than germline mutations in metabolic genes may predispose to cancers in organs that have a physiologic role in detecting hypoxia. Conditions that effectively lead to tissue hypoxia in hypoxia detecting tissues is one such mechanism. We propose that some of the common molecular and physiologic mechanisms in heritable forms of kidney cancer, namely detection of hypoxia, may play a role in the genesis of sporadic kidney cancer. We survey evidence suggesting that the mechanism of some recognized risk factors of kidney cancer, such as smoking and obesity, may be due in part to tissue hypoxia, reflecting physiologic detection of hypoxia gone awry.

Carcinoma, Renal Cell↗

PubMed2005

The role of IL-6 and STAT3 in inflammation and cancer.

The defense of the host from foreign pathogens is the commonly accepted function of the vertebrate immune system. A complex system consisting of many differing cells and structures communicating by both soluble and cell bound ligands, serves to protect the host from infection, and plays a role in preventing the development of certain types of tumours. Numerous signalling pathways are involved in the coordination of the immune system, serving both to activate and attenuate its responses to attack. The ability of the immune system, specifically those cells involved in acute inflammatory responses, to mediate the directed (and sometimes indirect) killing of cells and pathogens, make it a potential threat to host survival. Furthermore, the production and release of various survival factors such as the pleiotropic cytokine IL-6, a major mediator of inflammation and activator of signal transducer and activator of transcription 3, serves to block apoptosis in cells during the inflammatory process, keeping them alive in very toxic environments. Unfortunately, these same pathways serve also to maintain cells progressing towards neoplastic growth, protecting them from cellular apoptotic deletion and chemotherapeutic drugs. Here, we discuss the relationships between cancer and inflammation, and some of the molecular mechanisms involved in mediating the unintended consequences of host defense and tumour survival.

Drug Resistance, Neoplasm↗

PubMed2005

Enforced expression of superoxide dismutase 2/manganese superoxide dismutase disrupts autocrine interleukin-6 stimulation in human multiple myeloma cells and enhances dexamethasone-induced apoptosis.

Autocrine pathways of proliferative and anti-apoptotic growth factors represent a serious impediment to the treatment of many types of tumors. In particular, interleukin-6 (IL-6), a pleiotropic cytokine known to play a critical role in the survival and growth of multiple myeloma cells, participates in an autocrine stimulation loop that serves to inhibit the induction of apoptosis during chemotherapy. Manganese superoxide dismutase (MnSOD) is an important antioxidant enzyme encoded by the SOD2 gene that attenuates oxidative free radicals in the mitochondria by catalyzing the formation of hydrogen peroxide from superoxide radicals. Transcription factor activity and binding is influenced by the oxidative state of cells, and dysregulation of MnSOD levels can result in abnormal patterns of gene expression. In the human multiple myeloma cell line IM-9, an autocrine IL-6 loop exists, which enables the cell to resist the effects of dexamethasone, a common treatment for multiple myeloma. Here, we show that SOD2 expression is epigenetically silenced in IM-9 cells, and replacement of MnSOD reduces cell proliferation and partially restores susceptibility to dexamethasone. The restoration of MnSOD also serves to decrease the expression levels of IL-6 by reducing the ability of activator protein-1, an important mediator of IL-6 expression in multiple myeloma cells, to bind to its enhancer site. These results show the importance of free radical-mediated dysregulation of autocrine growth factor loops in tumor cells and their effect on cell growth and response to chemotherapy.

Apoptosis↗

PubMed2005

Interleukin 6 supports the maintenance of p53 tumor suppressor gene promoter methylation.

A strong association exists between states of chronic inflammation and cancer, and it is believed that mediators of inflammation may be responsible for this phenomenon. Interleukin 6 (IL-6) is an inflammatory cytokine known to play a role in the growth and survival of many types of tumors, yet the mechanisms employed by this pleomorphic cytokine to accomplish this feat are still poorly understood. Another important factor in tumor development seems to be the hypermethylation of CpG islands located within the promoter regions of tumor suppressor genes. This common epigenetic alteration enables tumor cells to reduce or inactivate the expression of important tumor suppressor and cell cycle regulatory genes. Here we show that in the IL-6-responsive human multiple myeloma cell line KAS 6/1, the promoter region of p53 is epigenetically modified by methyltransferases, resulting in decreased levels of expression. Furthermore, cells treated with IL-6 exhibit an increase in the expression of the DNA maintenance methylation enzyme, DNMT-1. The DNA methyltransferase inhibitor zebularine reverses the methylation of the p53 promoter, allowing the resumption of its expression. However, when zebularine is withdrawn from the cells, the reestablishment of the original CpG island methylation within the p53 promoter does not occur in the absence of IL-6, and cells which do not receive IL-6 eventually die, as p53 expression continues unchecked by remethylation. Interestingly, this loss of viability seems to involve not the withdrawal of cytokine, but the inability of the cell to resilence the promoter. Consistent with this model, when cells that express IL-6 in an autocrine fashion are subjected to identical treatment, p53 expression is reduced shortly after withdrawal of zebularine. Therefore, it seems IL-6 is capable of maintaining promoter methylation thus representing one of the possible mechanisms used by inflammatory mediators in the growth and survival of tumors.

Apoptosis↗

PubMed2005

Epigenetic silencing of manganese superoxide dismutase (SOD-2) in KAS 6/1 human multiple myeloma cells increases cell proliferation.

The generation of reactive oxygen species (ROS) by mitochondrial electron transport chain (ETC) and oxidative phosphorylation activity, has been linked to modifications of multiple molecular processes, including lipid peroxidation, signaling pathway and transcription factor modulation, and oxidative damage to DNA. Oxidative damage by endogenous ROS has been associated with the etiology of various pathological states. There are numerous reports that levels of manganese superoxide dismutase enzyme (MnSOD), an antioxidant enzyme responsible for the attenuation of ROS, are lowered in cancer cells, but the reasons for this reduction are poorly defined. Epigenetic silencing of genes involved in tumor suppression and DNA repair is known to occur in a variety of malignant cell types. Here we report that in the human multiple myeloma cell line KAS 6/1, the SOD-2 gene, encoding manganese superoxide dismutase, is epigenetically silenced as a result of promoter hypermethylation. The DNA methyltransferase inhibitor Zebularine reverses SOD-2 promoter methylation, increasing gene expression and enzyme levels. Infection of KAS 6/1 cells with a recombinant adenovirus carrying the MnSOD cDNA reduced the cell proliferation rate by approximately one-half, confirming the detrimental effects of epigenetic silencing of SOD-2 expression.

Cell Line, Tumor↗

PubMed2005

Nuclear receptors as negative modulators of STAT3 in multiple myeloma.

Multiple myeloma (MM) remains largely incurable despite conventional and high-dose therapies. Therefore, novel biologically based treatment approaches are urgently required. Particularly, STAT3 activated by IL-6 has a key role in preventing apoptosis and stimulating growth of multiple myeloma cells. Nuclear receptors, a distinct class of ligand-activated transcriptional factors, can interact and modify the function of transcriptional factors intrinsic to the cytokine signal transduction pathways. We have investigated regulation of two nuclear receptors, peroxisome proliferator-activated receptor gamma (PPARgamma) and estrogen receptor (ER), and their crosstalk with STAT3 in multiple myeloma. These results indicate that ligand-activated nuclear receptors can function as negative modulators of STAT3 through direct mechanisms, or in turn, by facilitating coregulators such as PIAS or SMRT. Therefore, different classes of nuclear receptors affect suppression of STAT3 functions through diverse mechanisms resulting in downregulating IL-6-mediated cell growth and gene expression. Given the importance of IL-6 in multiple myeloma, the estrogen receptor-STAT3 or PPARgamma-STAT3 interaction may have significant therapeutic implications in multiple myeloma.

Animals↗

PubMed2004

Co-operative functions between nuclear factors NFkappaB and CCAT/enhancer-binding protein-beta (C/EBP-beta) regulate the IL-6 promoter in autocrine human prostate cancer cells.

BACKGROUND: IL-6 is a growth and survival factor for prostate cancer cells through autocrine pathways. Here, we have systematically examined the transcriptional regulation mechanisms of IL-6 in autocrine prostate cancer cells. METHODS: RT-PCR and immunohistochemical staining were used to determine IL-6 production in the cells. Serial mutant IL-6 promoter luciferase reporters were generated and their transcriptional activities were examined. The transcription factors involved in IL-6 regulation were identified with super-shift EMSA. Overexpression of NFkappaB p65 and C/EBP-beta, and blockade of NFkappaB with IkappaBalpha or CAPE were performed to demonstrate the cooperation between NFkappaB p65 and C/EBP-beta in activation of IL-6. RESULTS: Transcription factor regulatory sites IL6-NFkappaB, IL6-C/EBP, IL6-CREB, and IL6-AP1, are responsive to constitutively activated IL-6 production in autocrine prostate cancer cell lines. Among these sites, IL6-AP1 and IL6-C/EBP appear most important, while IL6-NFkappaB shows the least effect for IL-6 promoter activity as determined by mutant IL-6 promoter luciferase reporter assay. Nevertheless, nuclear factor NFkappaB is activated and required. Such activation is minimally dependent upon the IL6-NFkappaB site, occurring through cooperation with other transcription factors that bind the IL-6 promoter. Cooperation between NFkappaB p65 and C/EBP-beta did not require a functional IL6-NFkappaB binding site. CONCLUSIONS: These data support a unique role for NFkappaB p65 as the primary trigger in autocrine production of IL-6 in prostate cancer cells. Furthermore, we describe a novel transcriptional activation mechanism for NFkappaB that is independent of its regulatory binding site, occurring through cooperation with other transcription factors that facilitate the neighboring regulatory site.

Base Sequence↗

PubMed2004

Epigenetic silencing of the human nucleotide excision repair gene, hHR23B, in interleukin-6-responsive multiple myeloma KAS-6/1 cells.

During tumorigenesis, selective proliferative advantage in certain cell subsets is associated with accumulation of multiple genetic alterations. For instance, multiple myeloma is characterized by frequent karyotypic instability at the earliest stage, progressing to extreme genetic abnormalities as the disease progresses. These successive genetic alterations can be attributed, in part, to defects in DNA repair pathways, perhaps based on epigenetic gene silencing of proteins involved in DNA damage repair. Here we report epigenetic hypermethylation of the hHR23B gene, a key component of the nucleotide excision repair in response to DNA damage, in interleukin-6 (IL-6)-responsive myeloma KAS-6/1 cells. This hypermethylation was significantly abated by Zebularine, a potent demethylating agent, with a consequent increase in the hHR23B mRNA level. Subsequent removal of this drug and supplementation with IL-6 in the culture medium re-established DNA hypermethylation of the hHR23B gene and silencing of mRNA expression levels. The inclination of DNA to be remethylated, at least within the hHR23B gene promoter region, reflects an epigenetic driving force by the cytogenetic/tumorigenic status of KAS-6/1 myeloma. The IL-6 response of KAS-6/1 myeloma also raises a question of whether the proneoplastic growth factor, such as IL-6, supports the epigenetic silencing of important DNA repair genes via promoter hypermethylation during the development of multiple myeloma.

Base Sequence↗

PubMed2004

NF-kappaB activates IL-6 expression through cooperation with c-Jun and IL6-AP1 site, but is independent of its IL6-NFkappaB regulatory site in autocrine human multiple myeloma cells.

IL-6 stimulates the growth and survival of a variety of tumors. In multiple myeloma (MM), IL-6 prevents spontaneous, drug-induced, and Fas-induced apoptosis. The sources of IL-6 in multiple myeloma appear to be both autocrine and paracrine in nature, with autocrine MM cells exhibiting a constitutively activated expression of the cytokine. Here we present a systematic analysis of the functional roles of the four major transcriptional regulatory sites present in the IL-6 promoter region, IL6-NFkappaB, IL6-C/EBP, IL6-CREB and IL6-AP1. Among these regulatory sites, IL6-AP1 is the most important cis-regulatory site, and plays a vital role in the constitutive expression of IL-6 in IM9 cells. Conversely, the IL6-CREB site, when bound by the transcription factor CREB, exhibits a repression of IL-6 autocrine expression, a result of possible steric hinderence of C/EBP-beta, due to the close proximity and site overlap between the IL6-C/EBP and IL6-CREB sites. Uniquely, although the presence of NF-kappaB protein is fundamental for constitutive expression of IL-6, a functional NF-kappaB site on the IL-6 promoter region is not required. The mechanism of NF-kappaB activation of IL-6 appears to occur through the cooperation with c-Jun protein, that constitutively occupies the IL6-AP1 site, and this indicates a novel transcriptional mechanism for NF-kappaB in the activation of NF-kappaB-driven genes.

CCAAT-Enhancer-Binding Protein-beta↗

PubMed2004

Microarray analysis of epigenetic silencing of gene expression in the KAS-6/1 multiple myeloma cell line.

The epigenetic control of gene transcription in cancer has been the theme of many recent studies and therapeutic approaches. Carcinogenesis is frequently associated with hypermethylation and consequent down-regulation of genes that prevent cancer, e.g., those that control cell proliferation and apoptosis. We used the demethylating drug zebularine to induce changes in DNA methylation, then examined patterns of gene expression using cDNA array analysis and Restriction Landmark Genomic Scanning followed by RNase protection assay and reverse transcription-PCR to confirm the results. Microarray studies revealed that many genes were epigenetically regulated by methylation. We concluded that methylation decreased the expression of, or silenced, several genes, contributing to the growth and survival of multiple myeloma cells. For example, a number of genes (BAD, BAK, BIK, and BAX) involved in apoptosis were found to be suppressed by methylation. Sequenced methylation-regulated DNA fragments identified by Restriction Landmark Genomic Scanning were found to contain CpG islands, and some corresponded to promoters of genes that were regulated by methylation. We also observed that after the removal of the demethylating drug, the addition of interleukin 6 restored CpG methylation and re-established previously silenced gene patterns, thus implicating a novel role of interleukin 6 in processes regulating epigenetic gene repression and carcinogenesis.

Cell Line, Tumor↗

PubMed2004

Tyrosine phosphorylation of the Janus kinase 2 activation loop is essential for a high-activity catalytic state but dispensable for a basal catalytic state.

The phosphorylation of an "activation loop" within protein kinases is commonly associated with establishing catalytic competence, and phosphorylation of the Tyr(1007) residue in the activation loop of Janus kinase 2 (JAK2) has been shown to be essential for intracellular propagation of cytokine-initiated signaling. We provide evidence for the presence of a basal activity state of JAK2, which was observed in the absence of activation loop phosphorylation. Phosphorylation of the JAK2 activation loop was essential for conversion to the high-activity state, characterized by high-efficiency ATP utilization during autophosphorylation. Mutagenesis of activation loop tyrosine residues Tyr(1007/1008) to phenylalanine residues impaired, but did not abolish, the enzyme's ability to autophosphorylate. The activation loop mutant JAK2 could also transphosphorylate an inactive JAK2 fragment coexpressed in Sf21 cells, providing evidence of exogenous substrate phosphorylation. The mutant enzyme remained in a basal activity state characterized by low-efficiency ATP utilization during autophosphorylation. Mutagenesis of a critical Lys(882) residue to a glutamate residue abolished all evidence of kinase activity, confirming that the observed activity of Tyr-to-Phe mutants was not due to another kinase. Our data are consistent with the proposal that JAK2 is an inefficient but active enzyme in the absence of activation loop phosphorylation and is capable of conversion to a high-activity state by autophosphorylation under physiological ATP concentrations. This theoretically precludes the need for an upstream activating kinase. The activation process of JAK2 may be envisioned as a multistate process involving at least two kinetically distinct states of activity.

Adenosine Triphosphate↗

PubMed2004

Activation of discoidin domain receptor 1 isoform b with collagen up-regulates chemokine production in human macrophages: role of p38 mitogen-activated protein kinase and NF-kappa B.

Macrophages produce an array of proinflammatory mediators at sites of inflammation and contribute to the development of inflammatory responses. Important roles for cytokines, such as IL-1 or TNF-alpha, and bacterial products, such as LPS, in this process have been well documented; however, the role for the extracellular matrix proteins, such as collagen, remains unclear. We previously reported that discoidin domain receptor 1 (DDR1), a nonintegrin collagen receptor, is expressed during differentiation of human monocytes into macrophages, and the interaction of the DDR1b isoform with collagen facilitates their differentiation via the p38 mitogen-activated protein kinase (MAPK) pathway. In this study, we report that the interaction of DDR1b with collagen up-regulates the production of IL-8, macrophage inflammatory protein-1alpha, and monocyte chemoattractant protein-1 in human macrophages in a p38 MAPK- and NF-kappaB-dependent manner. p38 MAPK was critical for DDR1b-mediated, increased NF-kappaB trans-activity, but not for IkappaB degradation or NF-kappaB nuclear translocation, suggesting a role for p38 MAPK in the modification of NF-kappaB. DDR1b-mediated IkappaB degradation was mediated through the recruitment of the adaptor protein Shc to the LXNPXY motif of the receptor and the downstream TNFR-associated factor 6/NF-kappaB activator 1 signaling cascade. Taken together, our study has identified NF-kappaB as a novel target of DDR1b signaling and provided a novel mechanism by which tissue-infiltrating macrophages produce large amounts of chemokines during the development of inflammatory diseases. Intervention of DDR1b signaling may be useful to control inflammatory diseases in which these proteins play an important role.

Adaptor Proteins, Signal Transducing↗

PubMed2004

Activating mutations in STAT3 and STAT5 differentially affect cellular proliferation and apoptotic resistance in multiple myeloma cells.

Multiple Myeloma (MM) is a progressive malignancy with poor prognosis, commonly treated by the use of the glucocorticoid Dexamethasone. Myeloma cells resist Dexamethasone induced apoptosis when exposed to IL-6 or IGF-1, both of which are known to activate several signaling cascades. For the first time, we show the actual contribution of downstream mediators, i.e., activated STAT factors, independent of the contribution of their upstream signaling pathways, on the proliferation and Dexamethasone rescue effects of IL-6 and IGF-1 in Multiple Myeloma. Retroviral transduction of cytokine dependent myeloma cells with activated STAT transcription factor constructs overcomes the cells dependence on cytokines for growth, allowing proliferation even in very low serum levels. However, the rescue of these previously cytokine dependent cells with activated STATs does not result in an increase in resistance to Dexamethasone induced apoptosis. Despite the presence of activated STAT3 and STAT5a, apoptosis is induced upon exposure to micromolar levels of Dexamethasone, and IL-6 or IGF-1 is still required to rescue the cells. The ability of these factors to block apoptosis is abrogated by the addition of PI-3 Kinase specific inhibitors, but not inhibitors that target the MAP Kinase pathway. However, ectopic expression of activated STAT3 results in partial rescue from apoptosis of cells treated with FAS ligand. Our data suggests that mechanisms of resistance to induced apoptosis and cellular proliferation are separate and distinct in cytokine dependent myeloma cells.

Anti-Inflammatory Agents↗