CK2-dependent C-terminal phosphorylation at T300 directs the nuclear transport of TSPY protein

TSPY (testis-specific protein, Y-encoded) is a member of the greater SET/NAP family of molecules with various functions, e.g., in chromatin remodeling, regulation of gene expression, and has been implicated to play a role in the malignant development of gonadoblastoma, testicular and prostate cancer. Here we demonstrate that the C-terminus has a functional role for the nucleo-cytoplasmatic shuttling of the TSPY protein. Using various combinations of in vitro mutagenesis and enhanced green fluorescent protein reporter gene-expression experiments we were able to show that while the deletion of C-terminus leads to a decreased stability and enhanced degradation of the protein, the selective mutation of a C-terminal CK2 phosphorylation site (T300) prevents the TSPY protein from entering the nucleus. We conclude that phosphorylation of the (T300) residue is a necessary and functional prerequisite for TSPY's transport into the nucleus reminding of comparable data from a related Drosophila molecule, NAP1.

T-/H-cadherin (CDH13): a new marker for differentiating podocytes

Cadherin molecules are known to be involved in various biological processes other than cell adhesion such as morphogenesis, cell-cell communication, cell recognition or cell signalling. While the classical cadherin molecule is characterized by an extracellular moiety, a transmembrane region and a variable cytoplasmic domain, T-/H-cadherin differs from this pattern due to the absence of a transmembrane region and a cytoplasmic domain, respectively. Its extracellular moiety is bound to the apical cell membrane by a glycosyl-phosphatidyl-inositol anchor and localized to lipid raft domains. As its molecular function and expression pattern is still not fully understood, we used a newly generated anti-T-/H-cadherin antiserum to study immunohistochemically the expression of T-/H-cadherin during the differentiation of foetal human glomeruli. At the early capillary loop stage a strong apical signal comes up for visceral epithelial cells of Bowman's capsule, which begin to differentiate towards podocytes. At the advanced capillary loop stage, when podocytes have become part of the glomerular filtration barrier, the expression pattern, however, becomes more distinct and most likely restricted to the foot processes of the podocytes. We thus postulate a functional role of T-/H-cadherin for the differentiation of the podocytes and the formation of the glomerular capillary network.