Abstract
NKIRAS1 and NKIRAS2 (also called as ÎşB-Ras) were identified as members of the atypical RAS family that suppress the transcription factor NF-ÎşB. However, their function in carcinogenesis is still controversial. To clarify how NKIRAS acts on cellular transformation, we generated transgenic mice in which NKIRAS2 was forcibly expressed using a cytokeratin 15 (K15) promoter, which is mainly activated in follicle bulge cells. The ectopic expression of NKIRAS2 was mainly detected in follicle bulges of transgenic mice with NKIRAS2 but not in wild type mice. K15 promoter-driven expression of NKIRAS2 failed to affect the development of epidermis, which was evaluated using the expression of K10, K14, K15 and filaggrin. However, K15 promoter-driven expression of NKIRAS2 effectively suppressed the development of skin tumors induced by treatment with 7,12-dimethylbenz(a)anthracene (DMBA)/12-O-tetradecanoylphorbol 13-acetate (TPA). This observation suggested that NKIRAS seemed to function as a tumor suppressor in follicle bulges. However, in the case of oncogenic HRAS-driven cellular transformation of murine fibroblasts, knockdown of NKIRAS2 expression drastically suppressed HRAS-mutant-provoked cellular transformation, suggesting that NKIRAS2 was required for the cellular transformation of murine fibroblasts. Furthermore, moderate enforced expression of NKIRAS2 augmented oncogenic HRAS-provoked cellular transformation, whereas an excess NKIRAS2 expression converted its functional role into a tumor suppressive phenotype, suggesting that NKIRAS seemed to exhibit a biphasic bell-shaped enhancing effect on HRAS-mutant-provoked oncogenic activity. Taken together, the functional role of NKIRAS in carcinogenesis is most likely determined by not only cellular context but also its expression level.
Highlights
NKIRAS1 and NKIRAS2 were identified as members of the atypical RAS family that suppress the transcription factor NF-ÎşB
RAP regulates cell adhesion mediated by cadherin and Âintegrin[11,12,13], and RHEB is involved in the activation of mammalian target of rapamycin complex 114
We previously demonstrated that NKIRAS predominantly bound to GTP without any agonistic stimulation such as epidermal growth factor (EGF) or platelet-derived growth factor (PDGF)[18]
Summary
NKIRAS1 and NKIRAS2 ( called as κB-Ras) were identified as members of the atypical RAS family that suppress the transcription factor NF-κB Their function in carcinogenesis is still controversial. K15 promoter-driven expression of NKIRAS2 effectively suppressed the development of skin tumors induced by treatment with 7,12-dimethylbenz(a) anthracene (DMBA)/12-O-tetradecanoylphorbol 13-acetate (TPA). This observation suggested that NKIRAS seemed to function as a tumor suppressor in follicle bulges. Abbreviations DMBA 7,12-Dimethylbenz(a)anthracene EGF Epidermal growth factor ERK Extracellular signal-regulated kinase IκB Nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor. NKIRAS1 and NKIRAS2 (NKIRAS1/2) were originally identified as members of the nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor (IκB)-interacting RAS superfamily. Phosphorylation of the RelA subunit at Ser-276 is essential for the transcriptional activation of NF-κB and accumulated in Ras mutant-driven colorectal cancer t issues[20,21]
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