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Aromatase inhibitors have played a central role in endocrine therapy for estrogen receptor ( ER)-positive breast cancer in postmenopausal women. However, factors predictive of the efficacy of aromatase inhibitors, and prognostic factors, both for early and late recurrence in women treated with adjuvant aromatase inhibitors have not been identified. Whole genome analysis identified that a TP53 gene mutation exists in ER-positive breast cancers, although the frequency of TP53 gene mutation in luminal tumors is lower compared with basal-like or human epidermal growth factor receptor type 2 ( HER2)-positive breast cancers. We examined expression of p53, as well as ER, progesterone receptor, HER2 and Ki-67 using immunohistochemistry in postmenopausal ER-positive breast cancer patients who were treated with aromatase inhibitors as adjuvant endocrine therapy. There were 53 (21%) tumors that contained 10% or more p53-positive cells. High p53 expression was positively correlated with tumor grade, HER2 score and Ki-67 expression. Significant association was observed between disease-free survival and high p53 expression in multivariate analysis ( P < 0.0001). Compared with women without recurrence, women with early recurrence had significantly higher p53 expression ( P < 0.0001), as did women with late recurrence ( P = 0.037). The present study demonstrates that p53 accumulation is a strong predictor of both early and late recurrence in ER-positive breast cancer patients treated with aromatase inhibitors as adjuvant endocrine therapy. TP53 gene alteration might be a key biological characteristic of ER-positive breast cancer. [ABSTRACT FROM AUTHOR]

Abstract: p73, a newly identified member of p53 family, locates at human chromosome 1p36.2-3, a region which is frequently deleted in a wide variety of human tumors including neuroblastoma. p73 is induced to be accumulated in response to a subset of DNA damaging agents such as cisplatin, and thereby promoting G1/S cell cycle arrest and/or apoptosis. Since the expression levels of p73 are kept extremely low under normal conditions, stabilization of p73 is critical for its effects on cell growth inhibition and apoptosis. Indeed, p73 is induced at protein level in SH-SY5Y neuroblastoma cells exposed to cisplatin. Several lines of evidence indicate that stress-induced post-translational modifications of p73 such as phosphorylation and acetylation lead to a marked extension of its half-life. p73 stability is regulated at least in part by proteasome-dependent degradation pathway, however, MDM2 which mediates ubiquitination and subsequent degradation of p53 by the 26S proteasome, does not promote the proteolytic degradation of p73, implying that the protein stability of p73 is regulated through a pathway distinct from that of p53. Although little is known about the regulation of p73 turnover, we are now beginning to understand the regulatory mechanisms by which p73 is induced to be stabilized in response to apoptotic stimuli, and exerts its pro-apoptotic activity. In this review, we discuss about the cellular proteins implicated in the stability control of p73. [Copyright &y& Elsevier]

Abstract: p73 responds to DNA damage and exerts its pro-apoptotic function. However, p73 might contribute to the development of drug-resistance in certain tumor cells. In this study, we found that p73 and MDM2 correlate with cisplatin-resistant phenotype of human epidermoid carcinoma-derived cells. p73 and MDM2 were kept at low levels in the cisplatin-sensitive KB-3-1 cells, whereas p53 was induced to be phosphorylated at Ser-15 in response to cisplatin. In contrast, p73 and MDM2 were expressed at higher levels, and cisplatin-mediated p53 phosphorylation was undetectable in the cisplatin-resistant KCP-4 cells. Enforced expression of p73 in KB-3-1 cells caused an accumulation of unphosphorylated form of p53 and MDM2, and conferred the cisplatin resistance. Collectively, our results suggest that a loss of the cisplatin sensitivity is at least in part due to a lack of cisplatin-induced p53 phosphorylation, and p73 might cooperate with MDM2 to be involved in this process. [Copyright &y& Elsevier]

p73, mapped to 1p36.2–3, is a p53-related tumor suppressor but is also induced by the oncogene products such as E2F1, raising a question whether p73 is a tumor suppressor gene or oncogene. p73 has several splicing variants including ΔNp73 which lacks the NH2-terminal transactivation domain. In developing neurons, ΔNp73 is expressed abundantly and seems to inhibit the pro-apoptotic function of p53. However, the role of TAp73 and ΔNp73 as well as their regulatory mechanism in cell growth and differentiation of neuroblastoma cells are poorly understood. We have found that TAp73 directly activates the transcription of endogenous ΔNp73 by binding to the TAp73-specific target element located at position-76 to 57 within the ΔNp73 promoter region. ΔNp73 was physically associated with TAp73α, TAp73β and p53, and inhibited their transactivation activities when used reporters of Mdm2, Bax or ΔNp73 itself in SAOS-2 cells. Overexpression of ΔNp73 in SH-SY5Y neuroblastoma cells promoted cell survival by competing with p53 and TAp73 itself. Thus, our results suggest that the negative feedback regulation of TAp73 by its target ΔNp73 is a novel autoregulatory system for modulating cell survival and death, that is also functioning in neuroblastoma cells. [Copyright &y& Elsevier]