Maspin sensitizes breast carcinoma cells to induced apoptosis

Abstract

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 ®rst 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 puri®ed 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 e ect, MDA-MB-435 cells were also transfected with maspin/PAI-1 and PAI-1/maspin chimeric constructs resulting from swapping the Nterminal 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 e ect of maspin on apoptosis is to be contrasted by the pro-survival e ect of several other serpins.

Maspin sensitizes prostate cancer cells to doxazosin-induced apoptosis

“…The present study provides proof-of-principle that maspin alters the sensitivity of prostate cancer cells to doxazosin. In a similar way, it was demonstrated that it could modify the ability of mammary MDA-MB-435 carcinoma cells to undergo apoptosis in response to staurosporine (Jiang et al, 2002). Our findings demonstrate an increased sensitivity of DU-145-maspin cells to the apoptotic actions of doxazosin, as evidenced by an increased apoptotic index and earlier caspase-3 cleavage.…”

“…The identification of maspin in breast epithelial cells provided a new insight on a possible mechanism of tumor suppression through inhibition of angiogenesis (Zhang et al, 2000), invasion of basement membranes and metastasis (Shi et al, 2001), and increased susceptibility of cancer cells to induced apoptosis (Jiang et al, 2002). The present study provides proof-of-principle that maspin alters the sensitivity of prostate cancer cells to doxazosin.…”

“…Maspin is classified as a class II tumor suppressor, since it is downregulated or silenced by hypermethylation in cancer cells (Domann et al, 2000), and suppresses tumor growth and metastasis in vivo and inhibits tumor invasion in vitro (Zou et al, 1994). Maspin also exerts a potent inhibitory action against osteolysis in a model of prostate cancer bone metastasis (Cher et al, 2003) and has been functionally linked to apoptosis of human breast and prostate cancer cells (Jiang et al, 2002). More recent evidence points to a role of maspin in angiogenesis regulation, as it reduces tumor microvessel density and endothelial cell migration in a prostate cancer xenograft model (Zhang et al, 2000).…”

Maspin protein expression correlates with tumor progression in non-muscle invasive bladder cancer

“…Maspin is a 42-kDa protein associated with various tumorrelated processes such as the inhibition of cell migration, cell invasion, angiogenesis, as well as improvement in cell adhesion and the induction of programmed cell death, thus classifying it as a tumor suppressor (8)(9)(10)(11)(12). Maspin expression has been observed in multiple tissues, e.g., epithelium of the breast, prostate, epidermis and lung (10,(22)(23)(24).…”

Maspin expression in CIN 3, microinvasive squamous cell carcinoma, and invasive squamous cell carcinoma of the uterine cervix

“…[8][9][10][11][12][13] Recent studies showed the regulation of maspin in response to androgen ablation of prostate cancer, which strongly implies that maspin plays a physiological role in growth inhibition 9 and engenders a sensitizing effect on apoptosis. 14 Oral squamous cell carcinomas that are immunopositive for maspin show a longer disease-free interval and overall survival period than tumors negative for maspin. Similarly, decreased maspin expression may significantly enhance the metastatic potential of stage I and II squamous cell carcinomas 15,16 of the tongue.…”