Splice variant PRKC-ζ(-PrC) is a novel biomarker of human prostate cancer

Previously, we have shown expression of the gene protein kinase C (PKC)-zeta (PRKCZ) to be characteristic of human prostate cancer (Cornford et al, 1999) where intensity of the protein PKC-ζ-a detected immunohistochemically is predictive of aggressive prostatic malignancy (P<0.001). RNAi gene knockdown, in vitro and in vivo behavioural studies and gene expression array analysis confirmed PRKCZ to be functionally involved in promoting the malignant prostatic phenotype (Yao et al, 2010). The gene PRKCZ is located on human chromosome 1 (at 1p36.33-p36.2) where it covers 136.21 kb on the direct strand. Containing 104 exons, it potentially encodes 46 structurally distinct splice variants designated in AceView as a–u and va–vy. During the last decade, the structure of human PRKCZ published by NCBI has undergone several major revisions as novel data have accrued. Nevertheless, important structure–function activities of the gene remain incomplete. Presently, the structure of PRKCZ splice variant ‘a' expressed in prostate cancer comprises 18 exons that are transcribed to a 2295 bp mRNA and translated into 592 amino acids yielding a 67.7 kD protein (Supplementary Table 1). Details of the current structural organisation of PRKCZ gene variant ‘a' is shown in Figure 1. Figure 1 (A) Full exonic sequence of NM variant ‘a' (NCBI database Build 36, April 2011). Genome exon numbers are in square brackets. Sizes of individual exons (blue boxes) and intervening introns are as shown. (B) Comparative structure of the 3′-terminal ... PKC isoenzymes are ancient proteins that appeared early during prokaryote evolution (Kruse et al, 1996; Manning et al, 2002) and are essential for the structural development and functional maintenance of multi-cellular organisms (Suzuki et al, 2003). Together, they comprise a complex family of some 14 serine–threonine kinases characterised by fundamental similarities in the structure of certain gene elements and in functional peptide domains (Hanks et al, 1988; Kofler et al, 2002). Broadly considered to be regulators of cellular homoeostasis and behavioural phenotypes (Dempsey et al, 2000), these enzymes are increasingly identified to be polyfunctional (Ohno and Nishizuka, 2002). High homology between apparently different members within the overall super family emphasises their common evolutionary origins but can obscure their subtly different functions that are crucial to understanding their roles in cancer cell survival and in designing biologically appropriate therapeutic agents (Ali et al, 2009). The genes for all of these enzymes characteristically encode multiple splice variants that are differentially expressed between tissues during morphogenesis (Patel et al, 2006; Dobkin-Bekman et al, 2010; Makary et al, 2011) and especially between malignant tissues and their benign histogenic counterparts (Lee et al, 2010; Urtreger et al, 2012). PRKCZ expression profoundly affects cellular behaviour (Le Good and Brindley, 2004; Xin et al, 2007), particularly in a diverse range of malignancies (Liu et al, 2009; Wu et al, 2009) where it modulates different biological mechanisms (Della Peruta et al, 2010; Luna-Ulloa et al, 2011; Valkov et al, 2011; Yu et al, 2011). Therefore, confirming its structure was considered as a prerequisite for understanding the role of this gene in prostate cancer. Thus, the aim of this study was to establish the detailed organisation of the PRKCZ gene expressed in prostate cancer and to test the hypothesis that alternative forms of PRKCZ might contribute cellular properties distinct from conventional PKC-ζ-a, hence promoting the malignant prostatic phenotype. We now report the retention and transcription of a normally intronic sequence within the 3′-terminal region of PRKCZ together with its translation into a novel protein (designated ‘PKC-ζ-PrC') that have been shown to be selective for human prostate cancer. This sequence is expressed simultaneously, but independently, from that of the conventional PKC-ζ-a. Inclusion of catalytic domains characteristically expressed in classic PKC-β and atypical PKC-ι- provides evidence that anomalous variants of protein kinase (PK) enzymes may promote the malignant phenotype of prostate cancer cells by mechanisms out-with normal regulatory processes.