Alternative titles; symbols
HGNC Approved Gene Symbol: UPK3B
Cytogenetic location: 7q11.23 Genomic coordinates (GRCh38): 7:76,510,552-76,516,522 (from NCBI)
UPK3B is a minor component of the apical plaques of mammalian urothelium that binds and dimerizes with uroplakin-1b (UPK1B; 602380), one of the major conserved urothelium membrane proteins. The other major conserved integral membrane proteins of urothelial plaques are UPK1A (611557), UPK2 (611558), and UPK3A (611559) (Deng et al., 2002).
By screening a human bladder cDNA library using bovine Upk3b, Deng et al. (2002) cloned UPK3B, which they called p35. They also cloned mouse and bovine Upk3b, which both share over 90% amino acid identity with UPK3B. Bovine Upk3b contains a signal peptide, a transmembrane domain, an N-terminal extracellular domain containing several N-glycosylation sites, and a short C-terminal cytoplasmic domain. The N-terminal extracellular domain contains an 80-amino acid sequence with homology to PMS2L11. Northern blot, Western blot, and immunohistochemical studies detected urothelium-specific expression of Upk3b mRNA and protein in bovine and mouse tissues.
Using cotransfection, followed by immunoprecipitation, Deng et al. (2002) demonstrated that UPK3B bound UPK1B but did not bind UPK1A, UPK2, and UPK3A. UPK3B was glycosylated, and cotransfection studies showed that the UPK3B/UPK1B complex was endoglycosidase H-resistant and able to exit the endoplasmic reticulum (ER), suggesting that the UPK3B/UPK1B complex forms in the ER and is exported to the cell surface. Upk3a-deficient mice showed a 6-fold increase in both Upk3b and Upk1b mRNAs, suggesting a coordinated regulation of Upk3b and Upk1b expression.
Deng et al. (2002) determined that the UPK3B gene contains 6 exons spanning 5 kb.
By genomic sequence analysis, Deng et al. (2002) mapped the UPK3B gene to chromosome 7q11.23 in close proximity to the PMS2L11 gene. They suggested that PMS2L11 and UPK3B may be related by duplication of an ancestral gene.
Deng, F.-M., Liang, F.-X., Tu, L., Resing, K. A., Hu, P., Supino, M., Hu, C.-C. A., Zhou, G., Ding, M., Kreibich, G., Sun, T.-T. Uroplakin IIIb, a urothelial differentiation marker, dimerizes with uroplakin Ib as an early step of urothelial plaque assembly. J. Cell Biol. 159: 685-694, 2002. [PubMed: 12446744] [Full Text: https://doi.org/10.1083/jcb.200204102]