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Open AccessArticle

Alternative Splicing of RAD6B and Not RAD6A is Selectively Increased in Melanoma: Identification and Functional Characterization

1
Karmanos Cancer Institute, Detroit, MI 48201, USA
2
Department of Oncology, Wayne State University School of Medicine, Detroit, MI 48201, USA
3
Champions Oncology, Rockville, MD 20850, USA
4
Pharmaceutical Sciences, Wayne State University, Detroit, MI 48201, USA
5
Department of Pathology, Wayne State University School of Medicine, Detroit, MI 48201, USA
*
Author to whom correspondence should be addressed.
Present address: Fralin Biomedical Research Institute, Virginia Tech Carilion School of Medicine, 2 Riverside Circle, Roanoke, VA 24016, USA
Cells 2019, 8(11), 1375; https://doi.org/10.3390/cells8111375
Received: 30 September 2019 / Revised: 28 October 2019 / Accepted: 31 October 2019 / Published: 1 November 2019
Rad6B, a principal component of the translesion synthesis pathway, and activator of canonical Wnt signaling, plays an essential role in cutaneous melanoma development and progression. As Rad6 is encoded by two genes, namely, UBE2A (RAD6A) and UBE2B (RAD6B), in humans, we compared their expressions in melanomas and normal melanocytes. While both genes are weakly expressed in normal melanocytes, Rad6B is more robustly expressed in melanoma lines and patient-derived metastatic melanomas than RAD6A. The characterization of RAD6B transcripts revealed coexpression of various splice variants representing truncated or modified functional versions of wild-type RAD6B in melanomas, but not in normal melanocytes. Notably, two RAD6B isoforms with intact catalytic domains, RAD6BΔexon4 and RAD6Bintron5ins, were identified. We confirmed that RAD6BΔexon4 and RAD6Bintron5ins variants are expressed as 14 and 15 kDa proteins, respectively, with functional in vivo ubiquitin conjugating activity. Whole exome sequence analysis of 30 patient-derived melanomas showed RAD6B variants coexpressed with wild-type RAD6B in all samples analyzed, and RAD6Bintron5ins variants were found in half the cases. These variants constitute the majority of the RAD6B transcriptome in contrast to RAD6A, which was predominantly wild-type. The expression of functional RAD6B variants only in melanomas reveals RAD6B’s molecular heterogeneity and its association with melanoma pathogenesis.
Keywords: melanoma; histone ubiquitination; alternative splicing; exon skipping; whole exome sequencing melanoma; histone ubiquitination; alternative splicing; exon skipping; whole exome sequencing
MDPI and ACS Style

Gajan, A.; Martin, C.E.; Kim, S.; Joshi, M.; Michelhaugh, S.K.; Sloma, I.; Mittal, S.; Firestine , S.; Shekhar, M.P.V. Alternative Splicing of RAD6B and Not RAD6A is Selectively Increased in Melanoma: Identification and Functional Characterization. Cells 2019, 8, 1375.

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