George C. Prendergast

Actin' up: RhoB in cancer and apoptosis

RhoB is a small GTPase that regulates actin organization and vesicle transport. It is required for signalling apoptosis in transformed cells that are exposed to farnesyltransferase inhibitors, DNA-damaging agents or taxol. Genetic analysis in mice indicates that RhoB is dispensable for normal cell physiology, but that it has a suppressor or negative modifier function in stress-associated processes, including cancer.

Loss of heterozygosity and tumor suppressor activity of Bin1 in prostate carcinoma.

The genetic events underlying the development of prostate cancer are poorly defined. c‐Myc is often activated in tumors that have progressed to metastatic status, so events that promote this process may be important. Bin1 is a nucleocytoplasmic adaptor protein with features of a tumor suppressor that was identified through its ability to interact with and inhibit malignant transformation by c‐Myc. We investigated a role for Bin1 loss or inactivation in prostate cancer because the human Bin1 gene is located at chromosome 2q14 within a region that is frequently deleted in metastatic prostate cancer but where no tumor suppressor candidate has been located. A novel polymorphic microsatellite marker located within intron 5 of the human Bin1 gene was used to demonstrate loss of heterozygosity and coding alteration in 40% of informative cases of prostate neoplasia examined. RNA and immunohistochemical analyses indicated that Bin1 was expressed in most primary tumors, even at slightly elevated levels relative to benign tissues, but that it was frequently missing or inactivated by aberrant splicing in metastatic tumors and androgen‐independent tumor cell lines. Ectopic expression of Bin1 suppressed the growth of prostate cancer lines in vitro. Our findings support the candidacy of Bin1 as the chromosome 2q prostate tumor suppressor gene. Int. J. Cancer 86:155–161, 2000.

Losses of the tumor suppressor BIN1 in breast carcinoma are frequent and reflect deficits in programmed cell death capacity

Oncogenic activation of MYC occurs often in breast carcinoma and is associated with poor prognosis. Loss or inactivation of mechanisms that restrain MYC may therefore be involved in tumor progression. In this study, we show that the MYC‐interacting adaptor protein BIN1 is frequently missing in malignant breast cells and that this loss is functionally significant. BIN1 was expressed in normal and benign cells and tissues but was undetectable in 6/6 estrogen receptor–positive or estrogen receptor–negative carcinoma cell lines examined. Similarly, complete or partial losses of BIN1 were documented in 30/50 (60%) cases of malignant breast tissue analyzed by immuno‐histochemistry or RT‐PCR. Abnormalities in the organization of the BIN1 gene were apparent in only a minority of these cases, suggesting that most losses were due to epigenetic causes. Nevertheless, they were functionally significant because ectopic BIN1 induced programmed cell death in malignant cells lacking endogenous BIN1 but had no effect on the viability of benign cells. We propose that loss of BIN1 may contribute to breast cancer progression by eliminating a mechanism that restrains the ability of activated MYC to drive cell division inappropriately. Int. J. Cancer 85:376–383, 2000. ©2000 Wiley‐Liss, Inc.Oncogenic activation of MYC occurs often in breast carcinoma and is associated with poor prognosis. Loss or inactivation of mechanisms that restrain MYC may therefore be involved in tumor progression. In this study, we show that the MYC-interacting adaptor protein BIN1 is frequently missing in malignant breast cells and that this loss is functionally significant. BIN1 was expressed in normal and benign cells and tissues but was undetectable in 6/6 estrogen receptor-positive or estrogen receptor-negative carcinoma cell lines examined. Similarly, complete or partial losses of BIN1 were documented in 30/50 (60%) cases of malignant breast tissue analyzed by immuno-histochemistry or RT-PCR. Abnormalities in the organization of the BIN1 gene were apparent in only a minority of these cases, suggesting that most losses were due to epigenetic causes. Nevertheless, they were functionally significant because ectopic BIN1 induced programmed cell death in malignant cells lacking endogenous BIN1 but had no effect on the viability of benign cells. We propose that loss of BIN1 may contribute to breast cancer progression by eliminating a mechanism that restrains the ability of activated MYC to drive cell division inappropriately.

Geranylgeranylated RhoB is sufficient to mediate tissue-specific suppression of Akt kinase activity by farnesyltransferase inhibitors

Farnesyltransferase inhibitors (FTIs) induce apoptosis by elevating the levels of geranylgeranylated RhoB (RhoB‐GG) in cells. However, the mechanism by which RhoB‐GG acts is unclear. Here we report that RhoB‐GG is sufficient to mediate the suppressive effects of FTIs on the activity of the survival kinase Akt‐1 in epithelial cells. This mechanism is tissue‐specific insofar as it does not operate in fibroblasts. We discuss how the cell survival functions of RhoB and Akt may be linked biochemically in certain cell types.

Knockout drug screens.

Cell lines that differ by a single genetic change show promise in drug screens to identify compounds with gene-selective properties.

15 Role of immunohistochemical loss of bin1/amphiphysin2 in prostatic carcinoma

Publisher Summary This chapter describes role of immunohistochemicai loss of Bin1/amphiphysin2 in prostatic carcinoma. In the prostate, Bin1 proteins are expressed robustly in the nucleus of normal cells, but they are often absent or mislocalized in cases of primary prostate adenocarcinoma and invariably absent in metastases. In vitro investigations with prostate-cancer cell lines show that ectopic expression of Bin1 proteins block proliferation and/or stimulate programmed cell death. Immunohistochemical analysis of Bin1 may have utility in discriminating the stage or prognosis of prostate cancers. The Bin1 gene encodes several alternately spliced adapter proteins that have been implicated in both vesicle dynamics and nuclear processes. There is considerable evidence that nuclear-localized Bin1 proteins have tumor suppressor and proapoptotic activities in cancer cells. Further, immunohistochemical analysis of Bin1 in prostate cancer may develop its potential as a prognostic marker or identifier for metastatic capacity.