Podocalyxin

Podocalyxin, a sialoglycoprotein, is thought to be the major constituent of the glycocalyx of podocytes in the glomerulus (Bowman's capsule).[1] It is a member of the CD34 family of transmembrane sialomucins.[2] It coats the secondary foot processes of the podocytes. It is negatively charged and thus functions to keep adjacent foot processes separated, thereby keeping the urinary filtration barrier open.[3] This function is further supported by knockout studies in mice which reveal an essential role in podocyte morphogenesis[4][5] and a role in the opening of vascular lumens and regulation of vascular permeability.[6][7][8] Of note, this is the only cell surface sialomucin knockout known to display a lethal phenotype.[4] Podocalyxin is also upregulated in a number of cancers and is frequently associated with poor prognosis.[5][9][10] Sialylated, O-glycosylated glycoforms of podocalyxin expressed by colon carcinoma cells possess L-selectin and E-selectin binding activity, and may be pivotal to the metastatic spread of colon carcinoma cells.[11][12][13] At the cellular level podocalyxin has also been shown to regulate the size and topology of apical cell domains and act as a potent inducer of microvillus formation.[14]