Melanocyte and Keratinocyte Carcinogenesis: p53 Family Protein Activities and Intersecting mRNA Expression Profiles

Abstract

Melanocytes and keratinocytes were analyzed for potential roles of p53, p73, and p63 tumor suppressor family proteins and of malignancy-specific gene expression changes in the etiology of multi-step cancer. Melanocytes expressed deltaNp73alpha, two p63 isoforms and p53. Although p21 and Noxa mRNA levels increased following DNA damage, p53 family member binding to p21 and Noxa DNA probes was undetectable, suggesting p53 family-independent responses. In contrast, keratinocytes expressed multiple isoforms each of p73 and p63 that were induced to bind p21 and Noxa DNA probes after ionizing (IR) or after ultraviolet B (UVB) irradiation, correlating with p21 and Noxa mRNA induction and with apoptosis. Interestingly, IR-resistant malignant melanocytes and keratinocytes both exhibited Noxa mRNA induction after UVB treatment, correlating with DNA binding of p53 family proteins to the Noxa probe only in keratinocytes. To uncover other malignancy-specific events, we queried mouse initiated keratinocyte clones for early changes that were exacerbated in malignant derivatives and also differentially expressed in human advanced melanoma versus normal melanocytes. Using a new method for ranking and normalization of microarray data for 5000 probe sets, 27 upregulated and 13 downregulated genes satisfied our query. Of these, the majority was associated with late-stage human cancers and six were novel genes. Thus, clonal lineage mouse models representing early through late cancer progression stages may inform the focus on early, potentially causal events from microarray studies of human cancers, facilitating prognosis and molecular therapy.

SCFβTrCP1 Activates and Ubiquitylates TAp63γ

“…1A, top). Since the p63 antibody is pan-specific, O3C keratinocytes were used as positive control for the p63 isoforms (23,24). Further, when the mRNA levels were examined using semiquantitative RT-PCR with TA-specific p63 primers, little change was observed (less than 0.5-fold) in TAp63 between the ␤TrCP1 ϩ/Ϫ and the ␤TrCP1 Ϫ/Ϫ MEFs (Fig.…”

P53 Family Activities in Development and Cancer: Relationship to Melanocyte and Keratinocyte Carcinogenesis

“…While the mechanisms underlying the roles of p63 and p73 in tumor suppression are not yet fully defined, their roles in homeostasis, differentiation and proliferation are indicative of tumor suppressive function. It has been shown that the relationship between p63 and p73 and epithelial carcinogenesis in null mice is consistent with models of sporadic cancer progression to SCC in keratinocyte lineages [39] and with many human tumors that also have reduced expression of p63 and p73 [40][41][42][43][44][45]. While deficiency of these proteins has been characterized in some tumors, overexpression of p63 and p73 isoforms has been found in others [46].…”

“…In order to begin to explain isoform-specific activities in tumor suppression, we have taken a global view of all three family members' expression and activities in mouse keratinocyte and melanocyte lineages during carcinogenesis [39]. We examined the total levels of each isoform, their ability to bind to DNA promoters of growth arrest and apoptosis genes, and the induction of downstream effector genes for growth arrest or apoptosis in response to DNA damage signals, i.e.…”

“…One approach is to use gene expression information from the mouse clonal lineage models (representing early through late cancer progression stages) to inform which genes are potentially causal events in human cancers. We queried microarray data for early gene expression changes that were exacerbated in malignant derivatives and also differentially expressed in human advanced melanoma vs. normal melanocytes [39]. Using a novel method for ranking and normalization of microarray data for five thousand probe sets, 27 upregulated and 13 downregulated genes satisfied our query.…”

p63 is an alternative p53 repressor in melanoma that confers chemoresistance and a poor prognosis

“…Previous studies of p63 in melano cytes are conflicting; mouse melanocytes express two isoforms of p63, TAp63 and either TAp63 or Np63 (KuleszMartin et al, 2005), and cultured human eye melanocytes do not ex press TP63 (Kilic et al, 2008). Neither of these studies were adequate biological correlates for human cutaneous melano cytes: mouse melanocytes predominantly reside in the hair fol licle within the dermis, mice do not spontaneously develop melanoma (Bardeesy et al, 2000;Merlino and Noonan, 2003), and the molecular biology of ocular melanoma is distinct from cutaneous melanoma (BelmarLopez et al, 2008;Sato et al, 2008;Shields et al, 2008).…”