Comprehensive characterization of protein 4.1 expression in epithelium of large intestine

Abstract

The protein 4.1 family consists of four members, 4.1R, 4.1N, 4.1B and 4.1G, each encoded by a distinct gene. All 4.1 mRNAs undergo extensive alternative splicing. Functionally, they usually serve as adapters that link actin-based cytoskeleton to plasma membrane proteins. It has been reported that 4.1 proteins are expressed in most animal cell types and tissues including epithelial cells and epithelial tissues. However, the expression of 4.1 proteins in large intestine has not been well characterized. In the present study, we performed RT-PCR, western blot and immunohistochemistry analysis to characterize the transcripts, the protein expression and cellular localization of 4.1 proteins in the epithelia of mouse large intestine. We show that multiple transcripts derive from each gene, including eight 4.1R isoforms, four 4.1N isoforms, four 4.1B isoforms and six 4.1G isoforms. However, at the protein level, only one or two major bands were detected, implying that not all transcripts are translated and/or the proteins do not accumulate at detectable levels. Immunohistochemistry revealed that 4.1R, 4.1N and 4.1B are all expressed at the lateral membrane as well as cytoplasm of epithelial cells, suggesting a potentially redundant role of these proteins. Our findings not only provide new insights into the structure of protein 4.1 genes but also lay the foundation for future functional studies.

4.1N-Mediated Interactions and Functions in Nerve System and Cancer

“…The functional decline of glutamatergic synapses is not observed in 4.1G/N double-mutant mice. Some AMPAR scaffold proteins substitute the 4.1G/N loss, which is the possible reason for the lack of phenotypic changes in 4.1G/N double-mutant mice ( Wozny et al, 2009 ; Zhang et al, 2014 ). Activation of GluR1-containing nucleus accumbens AMPARs in subregions of the brain nucleus accumbens enhanced the reinstatement of cocaine seeking.…”

“…The FERM domain of 4.1R contains phosphorylation sites and is regulated by PKC, protein kinase A, caseine, and tyrosine kinase ( Manno et al, 2005 ; Gauthier et al, 2011 ). 4.1N also contains the conserved phosphorylation sites ( Pearson and Kemp, 1991 ; Calinisan et al, 2006 ; Olsen et al, 2006 ; Zhang et al, 2014 ). In comparison with the 4.1N contractors, whether the protein 4.1N itself is phosphorylated in the phosphorylation events above is still unknown.…”