The observation that PADI2 is upregulated in the luminal subtype confirms previous gene expres sion data where PADI2 was identified as one of the top upregulated genes in luminal breast cancer lines com pared to basal lines. In order to test whether the observed correlation between PADI2 and HER2 Ponatinib ERBB2 would be retained at the protein level, we also tested a small sample of cell lines representing the four common breast cancer subtypes and found that PADI2 expression was only observed in the HER2 ERBB2 BT 474 and SK BR 3 lines. However, we did observe some discord ance seen between PADI2 transcript and protein levels, but we predict this difference may be due to post transcriptional regulatory mechanisms.

This prediction is based, in part, upon the observation that PADI2 possesses a long 3UTR that contains several AU rich elements that have been shown to bind the stabilizing regulatory factor HuR. HuR binding has been shown to enhance the stability of mRNAs involved in proliferation, while also playing a role in breast cancer, as cytoplasmic accumulation of HuR pro motes tamoxifen resistance in BT 474 cells and the stability of HER2 ERBB2 transcripts in SK BR 3 cells. Interestingly, from these studies, the level of HuR was reported to be high in both BT 474 and SK BR 3 cells, while it was relatively low in MCF7 cells. It is im portant to note that while we observed low levels of PADI2 protein expression in MCF7, recent work from our lab has confirmed the expression of PADI2 in MCF7 cells.

We also examined two mouse models of mammary tumorigenesis, the luminal MMTV neu and the basal MMTV Wnt 1, and found that, as predicted, PADI2 levels are highest in the HER2 ERBB2 overexpressing MMTV neu mice compared to normal mammary tissue and to hyperplastic and primary MMTV Wnt 1 tumors. Taken together, these findings indicate that PADI2 is predominantly expressed in luminal epithelial cells, and that there appears to be a strong relationship between PADI2 and HER2 ERBB2 expression in breast cancer. Subsequent studies are now underway to test whether PADI2 plays a functional AV-951 role in HER2 ERBB2 driven breast cancers, potentially by functioning as an inflam matory mediator. Previous studies have shown that the inhibition of PADI enzymatic activity by Cl amidine is effective in decreasing the growth of several cancer cell lines, and that admin istering the drug in combination with doxorubicin or the HDAC inhibitor SAHA can have synergistic cytotoxic effects on cells. Cl amidine is highly specific for all PADI enzymes, with dose dependent cytotoxicity and little to no effect in non cancerous cell lines.