Genomic Structure and Alternative Splicing of Type R2B Receptor Protein Tyrosine Phosphatases, and the Role of RPTP?
The type R2B receptor tyrosine phosphatase family, which includes RPTP?, PTP?, PTP? and PCP-2, has been linked to signal transduction, cell adhesion and neurite extension. These transmembrane molecules have an extracellular segment with several cell adhesive domains, and an intracellular segment containing a juxtamembrane, cadherin-like region, and two phosphatase domains, only the first of which is catalytically active. The expression of each of these genes is developmentally regulated, and each has distinct expression distribution patterns.
The genomic organization and alternative splicing of the type R2B genes was elucidated and compared. The human and mouse RPTP? genes are the largest of the RPTP genes. The mouse and human RPTP genes have 30 to 33 exons, and share a similar structure. The exons encoding the extracellular segment and the intracellular juxtamembrane ‘wedge’ region are separated by extremely large introns, while exons encoding the phosphatase domains are tightly clustered. The region with the least similarity among members of the R2B family was the wedge domain. In addition, all four genes have transcripts with alternatively spliced juxtamembrane regions, indicating a mechanism by which these genes could generate multiple protein isoforms with different binding or catalytic properties.
RPTP? is the most recently discovered R2B phosphatase. To identify potential protein substrates of RPTP?, a substrate-trapping mutant approach was used. A recombinant protein containing the juxtamembrane region and the first phosphatase domain was constructed with a mutation that generates a protein that is able to bind but not release substrates. This mutant protein was catalytically inactive, while the corresponding wild-type protein was catalytically active. GST pulldown assays with this mutant identified multiple proteins from the brain as potential substrates. Antibodies were used to identify these interacting proteins. RPTP? was found to bind ?-, ?- and ?-catenin, ?-actinin, pp120, desmoglein, and N- and E-cadherin. These results were extended by using a wild-type RPTP? recombinant protein to dephosphorylate proteins identified in the GST pulldown assays. RPTP? was able to dephosphorylate E-cadherin and pp120 in a dose-dependent manner. These proteins are components of intercellular adhesive junctions. This is the first evidence to link RPTP? to a specific biochemical function.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:protein phosphorylation alternative splicing gene structure cell adhesion
Date of Publication:01/01/2002