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Biomedical subjects

Graham Packham

Publications and source records attributed to Graham Packham.

25 records · Page 2Linked to original sources
PubMed2003

The nuclear BAG-1 isoform, BAG-1L, enhances oestrogen-dependent transcription.

BAG-1 is a multifunctional protein that interacts with a wide range of cellular targets including heat-shock proteins and some nuclear hormone receptors. BAG-1 exists as three major isoforms, BAG-1L, BAG-1M and BAG-1S. BAG-1L contains a nuclear localization signal, which is not present in the other isoforms, and is predominantly localized in the cell nucleus. Here we have investigated the effects of BAG-1 on function of the oestrogen receptor (ER), a key growth control molecule and target for hormonal therapy in breast cancer. We demonstrate that BAG-1L, but not BAG-1S or BAG-1M, increased oestrogen-dependent transcription in breast cancer cells. BAG-1L interacted with and stimulated the activity of both ER alpha and beta. Although BAG-1L and ERs colocalize to the nucleus, fusing BAG-1S to an heterologous nuclear localization sequence was not sufficient to stimulate transcription. Consistent with an important effect on receptor function, nuclear BAG-1 expression in breast cancers was associated with expression of the progesterone receptor, a transcriptional target of ERalpha, and was associated with improved survival in patients treated with hormonal therapy. These data suggest that BAG-1L is an important determinant of ER function in vitro and in human breast cancer.

Breast Neoplasms↗
PubMed2003

BAG-1 prevents stress-induced long-term growth inhibition in breast cancer cells via a chaperone-dependent pathway.

BAG-1 is a multifunctional protein that interacts with a wide range of cellular targets. There is accumulating evidence that overexpression of BAG-1 may play an important role in breast cancer; however, the functional consequences of BAG-1 expression and its mechanism of action in breast cancer cells have not been studied in detail. Here we demonstrate that BAG-1 overexpression completely protected breast cancer cells from apoptosis and long-term growth inhibition induced by heat shock and also partially protected cells from other stresses, including hypoxia, radiation, and chemotoxic drugs. BAG-1 exists as three protein isoforms, and all isoforms prevented stress-induced growth inhibition. This required a conserved lysine in the BAG-1S ubiquitin-like domain thought to be important for proteasome binding and COOH-terminal amino acids required for interaction with the chaperone molecules, Hsc70 and Hsp70. Although expression of BAG-1 was unaltered by heat shock, endogenous and overexpressed BAG-1S relocalized from the cytoplasm to the nucleus after heat shock. The endogenous BAG-1S.Hsc70/Hsp70 complex dissociated after heat shock but was maintained at a detectable level in cells overexpressing BAG-1S. BAG-1-mediated resistance to stress-induced growth inhibition is likely to have a major impact on the development and response to therapy of breast cancer. Targeting the interaction of BAG-1 with chaperones is an attractive strategy to counter the biological effects of BAG-1.

Apoptosis↗
PubMed2003

BAG-1: a multifunctional regulator of cell growth and survival.

BAG-1 is multifunctional protein which interacts with a wide range of cellular targets to regulate growth control pathways important for normal and malignant cells, including apoptosis, signaling, proliferation, transcription and cell motility. Of particular relevance to tumour cells, BAG-1 interacts with the anti-apoptotic BCL-2 protein, various nuclear hormone receptors and the 70 kDa heat shock proteins, Hsc70 and Hsp70. Interaction with chaperones may account for many of the pleiotropic effects associated with BAG-1 overexpression. Recent studies have shown that BAG-1 expression is frequently altered in malignant cells, and BAG-1 expression may have clinical value as a prognostic/predictive marker. This review summarises current understanding of molecular mechanisms of BAG-1 expression and function.

Amino Acid Sequence↗
PubMed2003

Regulation of tumour necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in Burkitt's lymphoma cell lines.

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) is a potent inducer of apoptosis in sensitive cells and may be suitable for novel anti-cancer therapies aimed at inducing apoptosis via the activation of TRAIL receptors on malignant cells. Here we have characterized the TRAIL sensitivity of a panel of Burkitt's lymphoma (BL) cell lines. Overall, 5/12 BL cell lines and 1/2 lymphoblastoid cell lines were sensitive to TRAIL-induced apoptosis, although only one BL cell line approached the sensitivity of Jurkat cells, a widely used model for TRAIL-induced apoptosis. Whereas, 4/5 of the Epstein-Barr virus (EBV)-negative cell lines were TRAIL sensitive, only 1/7 EBV-positive BL cell lines were TRAIL sensitive. However, isogenic BL cell lines with different EBV status were not differently sensitive to TRAIL, indicating that EBV is not a major determinant of TRAIL sensitivity. All cell lines expressed the death receptor (DR)5 TRAIL receptor, whereas expression of DR4 was more variable. Differences in the expression of downstream signalling molecules [Fas-associated death domain protein (FADD), caspase 8] and inhibitors [decoy receptor 1 (DcR1), cellular FLICE-like inhibitory protein (c-FLIP)] did not correlate with TRAIL sensitivity. Therefore, a subset of BL cell lines are sensitive to TRAIL-induced apoptosis, however, the molecular mechanism that determines responsiveness remains to be identified.

Antineoplastic Agents↗
PubMed2002

Differential signaling via surface IgM is associated with VH gene mutational status and CD38 expression in chronic lymphocytic leukemia.

The mutational status of tumor immunoglobulin V(H) genes is providing a powerful prognostic marker for chronic lymphocytic leukemia (CLL), with patients having tumors expressing unmutated V(H) genes being in a less favorable subset. However, the biologic differences correlating with V(H) gene status that could determine the clinical course of the disease are unknown. Here we show that differing responses to IgM ligation are closely associated with V(H) gene status. Specifically, 80% of cases with unmutated V(H) genes showed increased global tyrosine phosphorylation following IgM ligation, whereas only 20% of samples with mutated V(H) genes responded (P =.0002). There was also an association between response to IgM ligation and expression of CD38 (P =.015). The Syk kinase, critical for transducing B-cell receptor (BCR)- derived signals, was constitutively present in all CLL samples, and there was a perfect association between global phosphorylation and induction of phosphorylation/activation of Syk. Nonresponsiveness to anti-IgM could be circumvented by ligation of IgD (10 of 15 samples tested) or the BCR-associated molecule CD79alpha (12 of 15 samples tested). These results suggest that multiple mechanisms underlie nonresponsiveness to anti-IgM in CLL and that retained responsiveness to anti-IgM contributes to the poor prognosis associated with the unmutated subset of CLL. The prognostic power of the in vitro response to IgM ligation remains to be determined in a large series, but the simple technology involved may present an alternative or additional test for predicting clinical course.

ADP-ribosyl Cyclase↗
PubMed2002

Deregulated Bag-1 protein expression in human oral squamous cell carcinomas and lymph node metastases.

Bag-1 is an anti-apoptotic protein that promotes metastasis in some tumour cell types. To determine whether Bag-1 expression is altered in 64 oral squamous cell carcinomas, tumour samples were compared with 17 samples of normal oral epithelium. Normal oral epithelia had pronounced nuclear staining in the basal and maturation layers and weak cytoplasmic staining that was most pronounced in the basal and suprabasal layers. Oral squamous cell carcinomas demonstrated a tendency for reduced nuclear staining intensity (p=0.036). Cytoplasmic staining intensity was not significantly different between tumour and normal tissue. However, many tumours were observed to have less of a difference between nuclear staining intensity and cytoplasmic staining intensity than normal oral epithelium. Furthermore, in lymph node metastases, cytoplasmic Bag-1 staining was stronger in 8/13 cases than in corresponding primary tumours (p=0.021). Western blotting using nine oral primary carcinoma cell lines and four normal keratinocyte cultures showed that the isoforms Bag-1s, Bag-1M, and Bag-1L were expressed in normal and malignant oral epithelial cells. Bag-1L unique sequences were shown to adopt an exclusively nuclear, and predominantly nucleolar, localization by use of transiently transfected N-terminal Bag-1L-EGFP. However, levels of Bag-1L in carcinoma cells did not differ significantly from those of normal keratinocytes. Therefore the reduced nuclear staining observed in oral squamous cell carcinomas compared with normal epithelium may reflect changes in the localization of Bag-1 isoforms, rather than decreased expression of Bag-1L. Alterations in the relative proportions of Bag-1S, Bag-1M, and Bag-1L were detected in 6/9 oral carcinoma cell lines; 5/9 oral carcinoma cell lines had a significantly greater proportion of Bag-1M than normal keratinocytes and in another cell line, Bag-1L was significantly underrepresented. Overall, the results suggest that Bag-1 deregulation plays a role in oral carcinogenesis at two different stages: during primary carcinoma development and during lymph node metastasis.

Adult↗