In addition to CypA’s automatic malregulation in diverse cancers, CypA can be influenced in its expression by chemotherapeutic agents. Independent research groups demonstrated that treatment with chemotherapeutic agents, 5-aza-2-deoxycytidine (DAC), celecoxib, and 5-fluorouracil (5-FU), lowers CypA expression [[21, 29] and [30]]. On the contrary, our group found that cisplatin causes CypA overexpression and induces resistance to diverse chemotherapeutic agents including cisplatin (unpublished data). Upregulation

of CypA in cancer is not so KPT-8602 cost unusual; yet the GDC 0068 exact mechanisms of transcriptional alteration of CypA in cancer are still elusive. Initially, CypA gene together with those of glyceraldehyde 3-phosphate dehydrogenase, rRNA and beta-actin was considered one of the constitutively expressed house- keeping genes which do not respond to external

stimuli. Considering the chaperone activity of CypA protein, it is not surprising to find up-regulation of CypA gene in response to stresses that can cause protein damage or denaturation [35]. Since molecular regulatory mechanisms of CypA expression are poorly understood, it needs to be further studied whether the CypA up-regulaion in cancer is CB-839 nmr controlled by the same regulatory mechanisms of stress induction. If up-regulation of CypA in cancers is linked to p53 and HIF-1α, most well-characterized cancer-related transcriptional regulatory factors, has been sought by several groups. Choi et al. demonstrated that HIF-1α can upregulate CypA by HIF-1α binding to hypoxia response elements (HRE) in the CypA promoter region under hypoxic conditions [36]. Similarly, Gu et al. first showed that CypA is up-regulated during p53-induced apoptosis using quantitative proteomic profiling [37, 38]. They also proposed that transcription of CypA might be induced by activated p53. While no direct evidence has been reported that p53 is activated or stabilized by CypA, it is interesting over to note that PIN 1, another type of PPIases, stabilizes

p53 through affinity binding of PIN 1 to the p53′s proline rich domain (PRD) [39]. Our group recently discovered binding activity of CypA to p53 which leads to stabilization of p53 (unpublished data). Clinical implications of the overexpressed Cyclophilin A in cancers Upregulation of CypA in many cancer types dictates an advantage of CypA overexpression toward cancer development. While the exact roles of CypA in cancer cells are yet to be defined, understanding the precise function of CypA during tumor development will be critical to assess its potential as a target for therapeutic intervention. Positive growth effect by excessive CypA on cancer cells was first reported by Howard et al. They showed that overexpression of CypA in small cell lung cancer stimulates cancer cell growth, and knockdown of CypA slows cancer cell growth, independent of its effects on angiogenesis [17, 18]. Other roles of CypA have also been proposed. Qi et al.