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Publications and source records attributed to Shijie Sheng.
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Maspin, a noninhibitory serine protease inhibitor, exerts multifaceted tumor-suppressive effects. Maspin expression is associated with better differentiated phenotypes, better cancer prognosis, and better drug sensitivity. Consistently, maspin also correlates with increased expression of Bax and p21WAF1/CIP1. Interestingly, histone deacetylase 1 (HDAC1), a major HDAC responsible for histone deacetylation, was shown to interact with maspin in a yeast two-hybrid screening. In this study, we confirmed the maspin/HDAC1 interaction in human prostate tissues, in prostate cancer cell lines, and with purified maspin. We produced several lines of evidence that support an inhibitory effect of maspin on HDAC1 through direct molecular interaction, which was detected in both the nucleus and the cytoplasm. Both endogenously expressed maspin and purified maspin inhibited HDAC1. In contrast, small interfering RNA (siRNA) silencing of maspin in PC3 cells increased HDAC activity. Accordingly, maspin-transfected DU145 cells exhibited increased expression of HDAC1 target genes Bax, cytokeratin 18 (CK18), and p21(WAF1/CIP1), whereas maspin siRNA decreased CK18 expression in PC3 cells. The maspin effect on HDAC1 correlated with an increased sensitivity to cytotoxic HDAC inhibitor M344. Interestingly, glutathione S-transferase (GST, another maspin partner) was detected in the maspin/HDAC1 complex. Furthermore, a COOH-terminally truncated maspin mutant, which bound to HDAC1 but not GST, did not increase histone acetylation. Although HDACs, especially the highly expressed HDAC1, are promising therapeutic targets in cancer intervention, our data raise a novel hypothesis that the endogenous inhibitory effect of maspin on HDAC1 is coupled with glutathione-based protein modification, and provide new leads toward future developments of specific HDAC1-targeting strategies.
Prostate cancer cells rely on androgen receptor (AR) for proliferation and survival. Therefore, curing prostate cancer will require elimination of AR. Although androgen is the natural ligand that activates AR, AR activity is also subject to regulation by growth factor/growth factor receptor-stimulated signaling pathways that control the cell cycle. Cell cycle regulatory proteins and protein kinases in signaling pathways affected by growth factors can lead to AR activation in the absence of androgen. While downstream signaling proteins such as cyclins, cyclin-dependent kinases (CDKs), and pRB can modulate AR activity, upstream signaling pathways involving protein kinases such as mitogen-activated protein kinases, protein kinase A, and protein kinase B/Akt can affect post-translational modification of AR to affect not only AR function but also AR stability. Calcium and calmodulin (CaM), essential for proliferation and viability of a number of cells, including prostate cancer cells, play an important role in AR expression, stability, and function. CaM affects AR partly by interacting directly with AR and partly by activating protein kinases such as Akt and DNA-PK that can phosphorylate AR. The ubiquitin/26S proteasome pathway responsible for timely destruction of cell cycle regulatory proteins whose levels impede cell cycle progression also induces AR expression by activating NF-kappaB, and promotes AR activity by participating in the assembly of an AR transcription complex. Maspin, a serine protease inhibitor that is known mostly for its role as a tumor suppressor can also regulate AR intracellular localization and function by competing with AR for binding to the chaperone protein Hsp90 and co-repressor HDAC1, respectively. This perspective reviews the experimental evidence implicating these diverse cellular processes in AR expression, stability, and/or function, and presents a rationale for disrupting these cellular processes as a viable option for the treatment of both the hormone-sensitive and the hormone-insensitive prostate cancer.
It is well documented that tumor suppressive maspin inhibits tumor cell invasion and extracellular matrix remodeling. Maspin is a cytosolic, cell surface-associated, and secreted protein in the serine protease inhibitor superfamily. Although several molecules have been identified as candidate intracellular maspin targets, the extracellular maspin target(s) remains elusive. Although maspin does not directly inhibit urokinase-type plasminogen activator (uPA) activity, we have shown evidence that maspin may block the pericellular proteolysis mediated by cell surface-associated uPA. In the current study, maspin significantly inhibited the Ca2+ reduction-induced detachment of DU145 cells. This maspin effect was associated with increased and sustained levels of mature focal adhesion contacts (FAC). We noted that maspin (a) colocalized with uPA and uPA receptor (uPAR), (b) enhanced the interaction between uPAR and low-density lipoprotein receptor related protein, and (c) induced rapid internalization of uPA and uPAR. The maspin effects on surface-associated uPA and uPAR required the interaction between uPA and uPAR. Further biochemical and biophysical analyses revealed that maspin specifically bound to pro-uPA with a deduced K(d) of 270 nmol/L and inhibited the plasmin-mediated pro-uPA cleavage. Interestingly, substitution of maspin p1' site Arg340 in the reactive site loop (RSL) with alanine not only abolished the binding to pro-uPA but also diminished the maspin effects on pro-uPA cleavage and cell detachment. These data show an important role of maspin RSL in regulating the uPA/uPAR-dependent cell detachment. Together, our data led to a new hypothesis that maspin may stabilize mature FACs by quenching localized uPA/uPAR complex before uPA activation.
Maspin is a 42-kDa novel serine protease inhibitor (serpin) with multifaceted tumor suppressive activities. To date, the consensus that maspin expression predicts a better prognosis still largely holds for breast, prostate, colon, and oral squamous cancers. Interestingly, however, more detailed analyses revealed a biphasic expression pattern of maspin in early steps of tumorigenicity and re-expression of maspin in dormant cancer metastatic revertants. These data suggest a sensitivity of maspin expression to changes of epithelial microenvironments, and a role of maspin in epithelial homeostasis. Experimental evidence consistently showed that maspin suppresses tumor growth, invasion and metastasis, induces tumor redifferentiation, and enhances tumor cell sensitivity to apoptosis. Maspin protein isolated from biological sources is a monomer, which is present as a secreted, a cytoplasmic, a nuclear, as well as a cell surface-associated protein. Nuclear maspin is associated with better prognoses of cancer. It is further noted that extracellular maspin is sufficient to block tumor induced extracellular matrix degradation, tumor cell motility and invasion, whereas intracellular maspin is responsible for the increased cellular sensitivity to apoptosis. Despite these exciting developments, the mechanistic studies of maspin have proven challenging primarily due to the lack of a prototype molecular model. Although the maspin sequence has overall homologies with other members in the serpin superfamily, it does not behave like a typical serpin, that is, non-inhibitory toward active serine proteases in solution. This novel feature is in line with the X-ray crystallographic evidence. Several recent studies dedicated to finding the maspin partners support a paradigm shift. The current review is intended to summarize these recent findings and discuss a new perspective of maspin in epithelial homeostasis.
Maspin, a 42 kDa protein, belongs to the serine protease inhibitor (serpin) superfamily and is more closely related to the ovalbumin-like serpin subfamily (ov-serpins). More than a decade after the discovery of the maspin gene, our pursuit of the molecular mechanisms of maspin revealed a significant divergence of maspin from other serpins. This review article summarizes recent advances in the identification of maspin-binding proteins and the potential underlying molecular mechanisms of maspin in tumor progression. Specifically, the molecular interactions of maspin with the cell surface-associated pro-urokinase-type plasminogen activator (pro-uPA) and intracellular histone deacetylase 1 (HDAC1) are highlighted. Our new evidence suggests a new paradigm that maspin acts as a serpin-like molecule to inhibit serine protease-like targets. From an evolution point of view, the uniquely important function of maspin in development and tumor progression is likely due to its ancestral sequence code, and accordingly, its novel "meta"-serpin structure. It is reasonable to hypothesize that the conservation of a serine protease-like catalytic center in many molecules requires the co-existence of endogenous antagonists. The unique inhibitory interaction of maspin with both HDAC1 and pro-uPA might not be substituted by other serpins that have evolved to acquire higher target specificities. Thus, tumor suppressive maspin offers a unique therapeutic opportunity.
Maspin, a mammary homologue of Serine Protease Inhibitors, has been shown to inhibit tumor progression and metastasis. Recently, its biological functions have been linked to its subcellular localization. Specifically, a nuclear, opposed to a combined nuclear and cytoplasmic localization has been associated with increased survival in human malignancies, including non-small cell lung cancer (NSCLC). However, it is not known whether transformation affects maspin expression during lung carcinogenesis, and whether its subcellular localization correlates with the morphological features of NSCLC. To address these questions, we studied maspin expression in a model of transformation of bronchial epithelial cells and in resected NSCLC. We found that decreased maspin accompanied chemical transformation of normal immortalized bronchial epithelial cells BEAS 2B. Immunohistochemistry revealed maspin expression to be virtually universal in NSCLC, occurring in 72/77 Adenocarcinoma (ACa), and 46/46 squamous cell carcinoma (SqCCa). SqCCa showed almost exclusively a combined nuclear-cytosolic stain. In contrast, nuclear maspin, but not combined nuclear-cytoplasmic maspin significantly correlated with low histological grade, lower proliferative rate, absence of invasion, and negative p53 stain in ACa. These data support the hypothesis that nuclear localization of maspin may stratify subtypes of NSCLC with favorable clinical-pathological features.
Maspin is a mammary serine protease inhibitor or serpin with tumor suppressive and antiangiogenic activity that inhibits tumor motility, invasion and metastasis, at least by its actions on cell membrane and extracellular matrix (ECM) proteins. Previous studies documented that the quinazoline-derived alpha1-adrenoceptor antagonist doxazosin affects the attachment and migration of prostate cancer cells. In this study, we investigated the effect of maspin overexpression on the apoptotic/antiadhesion response of prostate cancer cells to doxazosin. The response of maspin-overexpressing clones of human prostate cancer cells DU-145 to doxazosin was evaluated by determining cell viability, apoptosis and cell proliferation on the basis of the trypan blue exclusion assay/methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay, Hoechst staining and caspase-3 activation, and [(3)H]thymidine incorporation assay. Vascular endothelial growth factor (VEGF), transforming growth factor betaRII (TGFbetaRII), Smad4 (a TGFbeta intracellular effector) and bax expression was evaluated at the mRNA and protein level using reverse transcriptase-polymerase chain reaction and Western blotting, respectively. The effect of doxazosin on cell attachment of maspin-expressing prostate cancer cells was evaluated on collagen- and fibronectin-coated plates. Cell migration was assessed using the wounding assay. In response to tumor necrosis factor-related apoptosis-inducing ligand, DU-145-maspin expressing cells undergo apoptosis, via poly(ADP-ribose) polymerasecleavage and caspase-3 activation. DU-145-maspin cells exhibited higher sensitivity to doxazosin and an earlier temporal activation of caspase-3. The number of apoptotic cells detected in response to doxazosin was significantly higher compared to the neo control (P<0.0001). Doxazosin resulted in dramatic downregulation of the 189 isoform of VEGF in maspin transfectants, while a fivefold induction of Smad4 mRNA expression was detected in those cells after 24 h of treatment. Maspin overexpression in prostate cancer cells resulted in an increased ability to attach to ECM-coated plates, and doxazosin treatment considerably antagonized this effect by decreasing the attachment potential to collagen and fibronectin. The present study supports the ability of maspin to enhance the apoptotic threshold of prostate cancer cells to the quinazoline-based alpha1-adrenoceptor antagonist doxazosin. These findings may have therapeutic significance in the development of antiangiogenic targeting by doxazosin and derivative agents for advanced prostate cancer.
Maspin, a novel serine protease inhibitor, suppresses tumor progression in several cancer models, including an in vivo model for prostate cancer bone metastasis. However, the molecular mechanism of maspin remains illusive, primarily because its molecular targets are unknown. To this end, we used a full-length maspin cDNA bait to screen against both a primary prostate tumor cDNA prey library and a HeLa cDNA prey library by the yeast two-hybrid method. We found that heat shock protein 90, glutathione S-transferase (GST), and heat shock protein 70 interacted with maspin with the highest frequencies. We confirmed the maspin/GST interaction using purified proteins, human epithelial cell lines, and human prostate tissues. A maspin variant that has a point mutation of Arg(340) to Ala (Mas(R340A)) showed a significantly decreased affinity for GST. Although purified maspin had no effect on the activity of purified GST in vitro, intracellular interaction between endogenous maspin and GST correlated with an elevated total GST activity in both MDA-MB-435- and DU145-derived stably transfected cells. Consistently, tumor cells treated with purified wild type maspin, but not Mas(R340A), enhanced cellular GST activity. Maspin expression in cancer cell lines also correlated with decreased basal levels of reactive oxygen species (ROS). Furthermore, H(2)O(2) treatment not only induced GST expression but also increased intracellular maspin/GST interaction, which was inversely correlated with the level of ROS generation. Conversely, maspin knockdown by small interfering RNA increased the basal, as well as H(2)O(2)-induced, ROS generation. Furthermore, the maspin effect on ROS generation was completely abolished by a GST inhibitor, indicating an essential role of GST in maspin-mediated cellular response to oxidative stress. Consistently, oxidative stress-induced vascular endothelial growth factor A expression was significantly inhibited in maspin-expressing cells. Together, our data suggest a new mechanism by which maspin, through its direct interaction with GST, may inhibit oxidative stress-induced ROS generation and vascular endothelial growth factor A induction, thus preventing further adverse effects on tumor genetics and stromal reactivity.
Previously, we and others showed that broad spectrum pharmaceutical inhibition of matrix metalloproteinase (MMP) activity reduces intraosseous tumor burden and bone degradation in animal models of bone metastasis. Herein, we used specific assays to measure net enzymatic activities of individual MMPs during colonization of bone by prostate cancer cells. PC3 cells were injected into the marrow of human fetal femurs previously implanted in SCID mice. Net MMP-9 activity in bone tissues peaked 2 weeks after injection, coinciding with a wave of osteoclast recruitment. In contrast, MMP-2 and MT1-MMP activity did not change. In vitro, co-culture of PC3 cells with bone tissue led to activation of pro-MMP-9 and increases in secreted net MMP-9 activity. Activation of pro-MMP-9 was prevented by metalloprotease inhibitors but not by inhibitors of other classes of proteases. Ribozyme suppression of MMP-9 expression in PC3 cells did not affect pro-MMP-9 activation or net MMP-9 activity and did not affect the phenotype of bone tumors. siRNA targeting of MMP-9 expression in preosteoclasts in vitro demonstrated that tumor-induced preosteoclast motility was dependent on MMP-9 expression. These data suggest that osteoclast-derived MMP-9 may represent a potential therapeutic target in bone metastasis and provide a rationale for the development of MMP-9-specific inhibitors.
Previous studies have shown a statistically significant correlation between human carcinomas and monoclonal antibody detection of a Mycoplasma hyorhinis-encoded protein known as p37. A potential mechanism of p37 is that it might promote invasion and metastasis. Recombinant p37 enhanced the invasiveness of two prostate carcinoma and two melanoma cell lines in a dose-dependent manner in vitro, but did not have a significant effect on tumor cell growth. Furthermore, the increased binding to cell surfaces and the enhanced invasive potential of cancer cells from exposure to p37 could be completely reversed by preincubation of the cancer cells with an anti-p37 monoclonal antibody. Sequence comparisons, followed by three-dimensional molecular modeling, revealed a region of similarity between p37 and influenza hemagglutinin A, a sialic acid-binding protein that plays a critical role in viral entry. Binding of p37 to prostate carcinoma cells was found to be at least partially sialic acid dependent because neuraminidase treatment decreased this binding. Taken together, these observations suggest that M. hyorhinis can infect humans and may facilitate tumor invasiveness via p37. These results further suggest that p37 may be a molecular target for cancer therapy.
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Since the identification of the human maspin gene, a decade of extensive research revealed the promise of maspin both as a valuable molecular marker for the diagnosis and prognosis of many types of cancers, and as a tumor suppressor at the level of tumor growth, invasion, angiogenesis, metastasis, and tumor sensitivity to drug-induced apoptosis. This review is intended to summarize the consensus of these findings, and provide an overview of the current challenges toward the clinical application of maspin. Specifically, this review discusses several likely molecular mechanisms underlying (1) the differential regulation of maspin expression, and (2) the biological activities of maspin in tumor progression.
Maspin, a serine protease inhibitor (serpin), can suppress tumor growth and metastasis in vivo and tumor cell motility and invasion in vitro. This may occur through maspin-mediated inhibition of pericellular proteolysis. In a recent report, we provided evidence that maspin may also suppress tumor progression by enhancing cellular sensitivity to apoptotic stimuli. To our knowledge, maspin is the only proapoptotic serpin among all of the serpins implicated thus far in apoptosis regulation. The goal of the present study is to identify the specific target molecule(s), the modification of which by maspin renders tumor cells sensitive to chemotherapeutic agents. Our cellular, molecular, and biochemical studies demonstrate an essential role of Bax in the proapoptotic effect of maspin. First, Bax was up-regulated in maspin-transfected prostate and breast tumor cells, whereas the levels of other Bcl-2 family members including Bcl-2, Bcl-xl, and Bak remained unchanged. Second, on apoptosis induction, a greater amount of Bax was translocated from cytosol to mitochondria in maspin-transfected cells. After treatment with a Bax-silencing small interfering RNA, maspin-transfected cells became significantly more resistant to drug-induced apoptosis. Consistently, the release of cytochrome c and Smac/DIABLO from mitochondria was more responsive to apoptosis stimuli in maspin-transfected cells than in the mock-transfected cells. Third, the apoptosis induction of maspin-transfected cells was associated with increased activation of both caspase-8 and caspase-9. However, a caspase-9-specific inhibitor blocked the sensitization effect of maspin in a dose-dependent and time-dependent manner, demonstrating a rate-limiting role for caspase-9. In line with the central role of the Bax-mediated mitochondrial apoptotic pathway, maspin sensitized the apoptotic response of breast and prostate carcinoma cells to various drugs, ranging from death ligands to endoplasmic reticulum stress. The link between maspin and Bax up-regulation explains the loss of maspin-expressing tumor cells in invasive breast and prostate carcinomas. Our data reveal a novel mechanism for tumor suppressive maspin and suggest that maspin may be used as a modifier for apoptosis-based cancer therapy.
Emerging evidence indicates that tumor-associated proteolytic remodeling of bone matrix may underlie the capacity of tumor cells to colonize and survive in the bone microenvironment. Of particular importance, urokinase-type plasminogen activator (uPA) has been shown to correlate with human prostate cancer (PC) metastasis. The importance of this protease may be related to its ability to initiate a proteolytic cascade, leading to the activation of multiple proteases and growth factors. Previously, we showed that maspin, a serine protease inhibitor, specifically inhibits PC-associated uPA and PC cell invasion and motility in vitro. In this article, we showed that maspin-expressing transfectant cells derived from PC cell line DU145 were inhibited in in vitro extracellular matrix and collagen degradation assays. To test the effect of tumor-associated maspin on PC-induced bone matrix remodeling and tumor growth, we injected the maspin-transfected DU145 cells into human fetal bone fragments, which were previously implanted in immunodeficient mice. These studies showed that maspin expression decreased tumor growth, reduced osteolysis, and decreased angiogenesis. Furthermore, the maspin-expressing tumors contained significant fibrosis and collagen staining, and exhibited a more glandular organization. These data represent evidence that maspin inhibits PC-induced bone matrix remodeling and induces PC glandular redifferentiation. These results support our current working hypothesis that maspin exerts its tumor suppressive role, at least in part, by blocking the pericellular uPA system and suggest that maspin may offer an opportunity to improve therapeutic intervention of bone metastasis.
BACKGROUND: Maspin, a novel serine protease inhibitor, has been shown to inhibit prostate tumor cell motility and invasion in vitro and to inhibit prostate tumor growth and metastasis in vivo. Maspin expression in high-grade prostate carcinoma (PC) is reduced compared with that in low-grade PC. Interestingly, however, compared with low-grade PC, benign secretory prostate epithelial cells express significantly less maspin. This observation appears paradoxical to a putative tumor suppressive role of maspin in prostate carcinogenesis, and this finding issue needs to be clarified. METHODS: We examined maspin expression simultaneously in benign basal cells, benign secretory cells, high-grade prostate intraepithelial neoplasia (HGPIN), low-grade PC, and high-grade PC in 46 radical prostatectomy specimens plus 51 autopsy prostate glands by a combination of immunohistochemistry and in situ hybridization. RESULTS: Benign basal cells consistently expressed maspin at a high level. In PC, the loss of basolateral maspin expression coincides with loss of the basal cell layer. Maspin expression in secretory cells, on the other hand, appears to undergo a biphasic differential regulation, i.e., essentially absent in benign secretory cells, dramatically up-regulated in HGPIN, then progressively down-regulated through low-grade PC to high-grade PC. Maspin expression in PC is inversely correlated with tumor grade. Furthermore, maspin expression in HGPIN is inversely correlated with the Gleason's grade of the adjacent PC. CONCLUSIONS: An up-regulation of maspin expression precedes, rather than occurs at, the critical transition from premalignant prostate lesion of HGPIN to PC. Our data suggest maspin may mark an important transitional phase and play an important role in the premalignancy of the prostate gland.
Maspin, a novel serine protease inhibitor (serpin), suppresses the growth and metastasis of breast tumor in vivo. However, the underlying molecular mechanism is unclear. In the current study, we report the first evidence that endogenous maspin expression in mammary carcinoma cells MDA-MB-435 enhanced staurosporine (STS)-induced apoptosis as judged by the increased fragmentation of DNA, increased proteolytic inactivation of poly-[ADP-ribose]-polymerase (PARP), as well as the increased activation of caspase-8 and caspase-3. In parallel, recombinant maspin did not directly regulate the proteolytic activities of either caspase-3 or caspase-8 in vitro. Consistent with this result, maspin expressing normal mammary epithelial cells underwent more rapid STS-induced apoptosis as compared to breast carcinoma cells. Interestingly, maspin transfectant cells did not undergo spontaneous apoptosis in the absence of STS. Moreover, neither purified maspin protein added from outside nor endogenous maspin secreted to the cell culture media sensitized cells to STS-induced apoptosis. To investigate the structural determinants of maspin in its apoptosis-sensitizing effect, MDA-MB-435 cells were also transfected with maspin/PAI-1 and PAI-1/maspin chimeric constructs resulting from swapping the N-terminal and the C-terminal domains between maspin and PAI-1 (plasminogen activator inhibitor type 1). The resulting stable transfectant clones expressing maspin/PAI-1 and PAI-1/maspin, respectively, did not undergo spontaneous apoptosis, and were similarly inhibited as maspin transfectant cells in motility assay. Interestingly, however, expression of both maspin/PAI-1 and PAI-1/maspin in MDA-MB-435 cells failed to sensitize these cells to STS-induced apoptosis. Taken together, our evidence provides new insights into the complex molecular mechanisms of maspin that may suppress breast tumor progression not only at the step of invasion and motility, but also by regulating tumor cell apoptosis. The sensitizing effect of maspin on apoptosis is to be contrasted by the pro-survival effect of several other serpins.
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