BRCA1-associated tumors are characterized by an elevated genomic instability and peculiar expression profiles. Nevertheless, tailored treatments for BRCA1 mutation carriers have only been partially investigated up to now. The implementation of therapeutic strategies specific for these patients has been in part hindered by the paucity of proper preneoplastic and neoplastic BRCA1-deficient tumor cell models. In this study, we took advantage of the RNA interference technology to generate a series of partially transformed (HBL100) and tumorigenic (MCF7 and T47D) breast cancer cell lines in which BRCA1 expression was silenced at different levels. These cell models were probed by clonogenic assay for their response to several DNA-damaging agents commonly used in cancer therapy (mitomycin C, cisplatin, doxorubicin, and etoposide). Our models confirmed the peculiar sensitivity to interstrand cross-link inducers associated with BRCA1 deficiency. Intriguingly, the increased sensitivity to these compounds displayed by BRCA1-defective cells was not correlated with the extent of apoptotic cell death but rather associated to an increased fraction of growth-arrested, enlarged, multinucleated β-galactosidase-positive senescent cells. Overall, our results support a role for BRCA1 in the regulation of interstrand cross-link-induced premature senescence and suggest a reconsideration of the therapeutic power of mitomycin/platinum-based treatments in BRCA1 carriers. Moreover, our data further prompt the setup of strategies for the imaging of the senescence response in vivo.

Inactivation of the breast cancer susceptibility gene 1 (BRCA1) plays a significant role in the development of a subset of familial breast and ovarian cancers, but increasing evidence points to a role also in sporadic tumors. BRCA1 is a multifunctional nuclear protein involved in the regulation of many nuclear cellular processes, including DNA repair, cell cycle, transcription and chromatin remodeling. To identify novel proteins participating in the BRCA1 network, two-dimensional gel electrophoresis and MALDI-TOF mass spectrometry were used to compare the nuclear-enriched proteome map of BRCA1-deficient and BRCA1-proficient cell lines. Five differentially expressed polypeptides were identified and two of them, hnRNPA2B1 and KHSRP, turned out to be involved in mRNA and miRNA metabolism. qRT-PCR analyses indicated that the hnRNPA2B1 and KHSRP levels increased in response to BRCA1 loss and restoration of BRCA1 expression in BRCA1 null cells reverted hnRNPA2B1 and KHSRP up-regulation. Interrogation of publicly available transcriptional profiling datasets revealed that both genes were actually over-expressed in BRCA1 mutated tumors. Overall, our results indicate that BRCA1 modulates the expression of two proteins involved in the processing of RNA, highlighting the complex nature of BRCA1-associated tumor suppressor function and disclosing a novel mechanism by which BRCA1 may affect transcription.

Diagnostic and prognostic implications of endocrine differentiation were evaluated in 103 common gastric adenocarcinomas and undifferentiated carcinomas. Maturely differentiated exocrine and endocrine phenotypes were evaluated by using gastric exocrine and endocrine markers along with intestinal exocrine and endocrine markers. Immunohistochemical analysis revealed that 66 tumors (64%) were positive for generic endocrine markers such as chromogranin A and/or synaptophysin. The 14 patients with more than 20% tumor cells positive for at least 1 endocrine marker experienced a poorer prognosis than patients with no (n = 37) or 1% to 20% (n = 52) positivity. The 16 carcinomas expressing the maturely differentiated exocrine gastric phenotype significantly correlated with poorer outcome compared with carcinomas with mature exocrine intestinal (n = 22) or mixed/gastrointestinal (n = 64) phenotypes. Among tumors expressing chromogranin A and/or synaptophysin, the maturely differentiated endocrine gastric phenotype (n = 26) was a negative prognostic factor compared with mature endocrine intestinal (n = 21) and mixed/gastrointestinal (n = 5) phenotypes. Endocrine differentiation and maturely exocrine/endocrine gastric phenotypes are associated with an unfavorable prognosis and may identify subsets of patients for tailored therapy.

<div>Abstract<p>BRCA1-associated tumors are characterized by an elevated genomic instability and peculiar expression profiles. Nevertheless, tailored treatments for BRCA1 mutation carriers have only been partially investigated up to now. The implementation of therapeutic strategies specific for these patients has been in part hindered by the paucity of proper preneoplastic and neoplastic BRCA1-deficient tumor cell models. In this study, we took advantage of the RNA interference technology to generate a series of partially transformed (HBL100) and tumorigenic (MCF7 and T47D) breast cancer cell lines in which BRCA1 expression was silenced at different levels. These cell models were probed by clonogenic assay for their response to several DNA-damaging agents commonly used in cancer therapy (mitomycin C, cisplatin, doxorubicin, and etoposide). Our models confirmed the peculiar sensitivity to interstrand cross-link inducers associated with BRCA1 deficiency. Intriguingly, the increased sensitivity to these compounds displayed by BRCA1-defective cells was not correlated with the extent of apoptotic cell death but rather associated to an increased fraction of growth-arrested, enlarged, multinucleated β-galactosidase–positive senescent cells. Overall, our results support a role for BRCA1 in the regulation of interstrand cross-link–induced premature senescence and suggest a reconsideration of the therapeutic power of mitomycin/platinum-based treatments in BRCA1 carriers. Moreover, our data further prompt the setup of strategies for the imaging of the senescence response <i>in vivo</i>. [Mol Cancer Ther 2009;8(4):844–54]</p></div>