Study of sPDZD2 function using in vitro and in vivo approaches
Abstract of the thesis entitled
Study of sPDZD2 function using in vitro and in vivo
Tam Siu Man Tammy
For the degree of Master of Philosophy
at The University of Hong Kong
in August 2004
PDZD2 (PDZ Domain Containing 2, also named PAPIN, AIPC and PIN-1) is a ubiquitously expressed multi-PDZ domain protein. Subcellular localization studies show that PDZD2 is localized mainly in the endoplasmic reticulum. Sequence alignment reveals significant homology between PDZD2 and another multi-PDZ protein pro-IL-16. Pro-IL-16 undergoes proteolytic cleavage to generate a secreted protein IL-16. Similar to IL-16, PDZD2 is cleaved proteolytically to generate a 37 kDa secreted protein (named sPDZD2) in a caspase-3 dependent manner.
IL-16 and sPDZD2 are the only secreted PDZ-containing proteins reported so far. IL-16 is a growth factor of T-cells and a differentiation factor that helps to differentiate the pro-B cells into pre-B cells. Until now, the function of sPDZD2 is poorly known. Sequence similarity with IL-16 suggests that sPDZD2 may serve similar growth and/or differentiation function for some cell types.
To identify the cell types that sPDZD2 may play a functional role, western blot analysis of different mouse tissues was done previously and it was found that sPDZD2 is highly expressed in pancreas. In this study, Western blot analysis of INS-1E cells and immunohistochemical analysis of pancreatic sections revealed
that both the full length PDZD2 and sPDZD2 are expressed predominantly in insulin-positive beta cells. Based on these findings, it is suggested that sPDZD2 may serve as a growth and/or differentiation factor for pancreatic beta cells.
To study the in vitro function of sPDZD2, recombinant sPDZD2 protein was synthesized and assayed for growth and other effects on INS-1E cells. Cell viability assay showed that sPDZD2 could enhance beta cells survival at 10-7 M under low serum condition. In addition, sPDZD2 could stimulate insulin promoter activity and achieve maximal stimulation at 10-10 M. These results suggest that sPDZD2 may help to maintain pancreatic beta cells survival and play a regulatory role on insulin gene expression.
To v e r i f y t h e in vivo biological effects of sPDZD2, transgenic mice overexpressing sPDZD2 in pancreatic beta cells were generated. Four transgenic founders were obtained and at least one of them could successfully transmit the transgene in the germline. Further characterization of these mouse lines is needed to study the effect of sPDZD2 overexpression on beta cells. It is believed that the results obtained in these in vitro and in vivo studies can complement each other in understanding the role of sPDZD2 as a potential growth and/or differentiation factor for pancreatic beta cells.
(Word count: 389)
School:The University of Hong Kong
School Location:China - Hong Kong SAR
Source Type:Master's Thesis
Date of Publication:01/01/2005