Yes-associated protein (YAP) has been shown to positively regulate p53 family members and to be negatively regulated by the AKT proto-oncogene product in promoting apoptosis. On the basis of this function and its location at 11q22.2, a site of frequent loss of heterozygosity (LOH) in breast cancer, we investigated whether YAP is a tumor suppressor in breast. Examination of tumors by immunohistochemistry demonstrated significant loss of YAP protein. LOH analysis revealed that protein loss correlates with specific deletion of the YAP gene locus. Functionally, short hairpin RNA knockdown of YAP in breast cell lines suppressed anoikis, increased migration and invasiveness, inhibited the response to taxol and enhanced tumor growth in nude mice. This is the first report indicating YAP as a tumor suppressor, revealing its decreased expression in breast cancer as well as demonstrating the functional implications of YAP loss in several aspects of cancer signaling.

Background: The tissue-specific translation elongation factor eEF1A2 was recently shown to be a potential oncogene that is overexpressed in ovarian cancer. Although there is no direct evidence for an involvement of eEF1A2 in breast cancer, the genomic region to which EEF1A2 maps, 20q13, is frequently amplified in breast tumours. We therefore sought to establish whether eEF1A2 expression might be upregulated in breast cancer.

Yes-associated protein (YAP) regulates DNA damage and chemosensitivity, as well as functioning as a pro-growth, cell size regulator. For both of its roles, regulation by phosphorylation is crucial. We undertook an in vitro screen to identify novel YAP kinases to discover new signaling pathways to better understand YAP's function. We identified JNK1 and JNK2 as robust YAP kinases, as well as mapped multiple sites of phosphorylation. Using inhibitors and siRNA, we showed that JNK specifically phosphorylates endogenous YAP in a number of cell types. We show that YAP protects keratinocytes from UV irradiation but promotes UV-induced apoptosis in a squamous cell carcinoma. We defined the mechanism for this dual role to be YAP's ability to bind and stabilize the pro-proliferative ΔNp63α isoform in a JNK-dependent manner. Our report indicates that an evaluation of the expression of the different isoforms of p63 and p73 is crucial in determining YAP's function.

Translation elongation factor eEF1A, formerly known as EF-1␣, exists as two variant forms; eEF1A1, which is almost ubiquitously expressed, and eEF1A2, whose expression is restricted to muscle and brain at the level of whole tissues. Expression analysis of these genes has been complicated by a general lack of availability of antibodies that specifically recognize each variant form. Wasted mice (wst/wst) have a 15.8-kilobase deletion that abolishes activity of eEF1A2, but before this study it was unknown whether the deletion also affected neighboring genes. We have generated a panel of anti-peptide antibodies and used them to show that eEF1A2 is expressed at high levels in specific cell types in tissues previously thought not to express this variant, such as pancreatic islet cells and enteroendocrine cells in colon crypts. Expression of eEF1A1 and eEF1A2 is shown to be generally mutually exclusive, and we relate the expression pattern of eEF1A2 to the phenotype seen in wasted mice. We then carried out a series of transgenic experiments to establish whether the expression of other genes is affected by the deletion in wasted mice. We show that aspects of the phenotype such as motor neuron degeneration relate precisely to the relative expression of eEF1A1 and eEF1A2, whereas the immune system abnormalities are likely to result from a stress response. We conclude that loss of eEF1A2 function is solely responsible for the abnormalities seen in these mice.