∆Np63α and YB-1 functional interaction regulates proliferation and survival of normal and transformed keratinocytes

The p63 protein is a member of the p53 gene family [1].The TP63 gene encodes isoforms that contain (TA) or lack (∆N) a transactivation domain. ∆Np63α, a critical pro-proliferative factor and a marker of epidermal stemness, is the most commonly expressed p63 protein and is essential for morphogenesis of organs/tissues developing by epithelial-mesenchimal interactions such as the epidermis, teeth, hair and glands [2]. We have recently shown that ∆Np63α is a molecular partner of the Y-box binding protein 1 (YB-1). YB-1, a marker of malignant tumor, is a nucleic acid binding protein with pleiotropic functions, such as alternative splicing, regulation of transcription and translation. Although YB-1 is predominantly cytoplasmic, it is highly expressed in the nuclear compartment of proliferating keratinocytes and squamous carcinoma cells. Here we show that ∆Np63α induces the nuclear accumulation of post-translationally modified forms of YB-1, sumoylation and ubiquitination are both involved in this phenomenon. During keratinocyte differentiation, YB-1 silencing restrains cell proliferation. In proliferating HaCaT and squamous carcinoma cells, YB-1 knockdown causes dramatic cell death and detachment. Our observations suggest that ∆Np63α and YB-1 functional interaction is critically associated with the proliferation and survival of normal and transformed keratinocytes.