Ras‐induced melanoma transformation is associated with the proteasomal degradation of the transcriptional repressor ICER

Abstract

Activation of the mitogen-activated protein kinase (MAPK) pathway targets the putative tumor suppressor protein inducible cAMP early repressor (ICER) to ubiquitin-mediated proteasomal degradation [Yehia et al. JBC 2001; 276: 35272-35279]. We demonstrate that ICER proteasomal degradation is implicated in Ras/MAPK-mediated melanoma tumorigenesis. In a system using Tyr/Tet-Ras INK4a-/- transgenic mice and melanoma cells in culture termed R545 cells isolated from Tyr/Tet-Ras INK4a-/- mice [Chin et al. Nature 1999; 400: 468-472], melanoma genesis and melanoma maintenance is strictly dependent upon expression of H-RasV12G. We found that ICER protein was not expressed during melanoma genesis but was strongly expressed in regressing melanomas. Similarly in R545 cells, ICER protein expression was negatively regulated by H-RasV12G. The expression of ICER mRNA was not affected by H-RasV12G expression, suggesting that ICER regulation was post-translational. Indeed, pharmacological inhibition of Ras activity or the proteasome abolished the degradation of ICER caused by H-RasV12G expression indicating that RAS oncogene regulates the expression of ICER protein by targeting ICER to proteasomal degradation. By engineering clones of R545 melanoma cells stably transfected with ICER we were able to determine the prerequisite for Ras-induced tumorigenesis. The reconstitution of physiological levels of ICER showed a significant decrease in cell growth, as well as inhibition of anchorage-independent cell growth and tumorigenicity in nude mice. ICER was found to efficiently repress the expression of cyclin D1 in R545 cells due to the binding of ICER to the CRE in the cyclin D1 promoter. Taken together, we postulate that ICER protein might be targeted to degradation in human tumors where Ras is mutated.

Metabolic strategies of melanoma cells: Mechanisms, interactions with the tumor microenvironment, and therapeutic implications

“…For example, Healey et al. utilized Tyr/Tet‐Ras INK4a −/− transgenic mice, and R545 melanoma cells isolated from their tumors, to demonstrate that Ras‐mediated melanomas target the inducible cAMP early repressor (ICER) for proteasomal degradation (Healey, Crow, & Molina, ). Without functional ICER protein, the tumor cells upregulated the transcription of cyclin D1, an essential mediator of cell cycle progression (Healey et al., ).…”

“…utilized Tyr/Tet‐Ras INK4a −/− transgenic mice, and R545 melanoma cells isolated from their tumors, to demonstrate that Ras‐mediated melanomas target the inducible cAMP early repressor (ICER) for proteasomal degradation (Healey, Crow, & Molina, ). Without functional ICER protein, the tumor cells upregulated the transcription of cyclin D1, an essential mediator of cell cycle progression (Healey et al., ). Likewise, p53 mutations are relatively uncommon (~20%) in melanoma (Albino et al., ; Cancer Genome Atlas Network, ; Hodis et al., ; Volkenandt, Schlegel, Nanus, & Albino, ; Weiss, Schwechheimer, Cavenee, Herlyn, & Arden, ).…”

CSE1L Links cAMP/PKA and Ras/ERK pathways and regulates the expressions and phosphorylations of ERK1/2, CREB, and MITF in melanoma cells

“…Melanoma causes the majority of deaths related to skin cancer. The Ras/Raf/MEK/ERK and cAMP/PKA signal pathways are crucial for the progression of melanoma [17][18][19][20]36]. The cAMP pathway activates CREB, thereby inducing MITF expression [37].…”

“…The activation of ERK1/2 induces MITF phosphorylation, which in turn stimulates MITF activation; this consequently results in MITF instability and degradation [15,16]. The Ras/Raf/ERK signaling pathway is implicated in the malignant progression of various cancers including melanoma [17][18][19][20]. ERK1/2 activation induces the phosphorylation and activation of MITF [15,16,21].…”

Calcyclin‐binding protein/Siah‐1‐interacting protein as a regulator of transcriptional responses in brain cells

“…In the case of β‐catenin‐driven transcription, CacyBP/SIP is an adaptor protein that facilitates β‐catenin degradation by its Siah‐1‐mediated ubiquitination (Matsuzawa and Reed, ). A similar mechanism that operates by destabilizing transcriptional activators or repressors might modulate CRE‐ and/or NFAT‐driven transcription (Liu et al, ; Sen and Snyder, ; Healey et al, ). Alternatively, CacyBP/SIP‐facilitated degradation of β‐catenin might affect CRE and/or NFAT.…”