Incorporation of leucocyte GPI-anchored proteins and protein tyrosine kinases into lipid-rich membrane domains of COS-7 cells
Abstract
Several human leucocyte surface glycoproteins and two lymphoid protein kinases were transiently expressed in monkey COS-7 fibroblastoid cells. All glycosylphospha-tidylinositol (GPI)-anchored proteins (CD14, CD16B, CD48, CD59, CD87 and GPI-anchored versions of CD2 and CD25) and protein tyrosine kinase (PTK) Lck but not transmembrane proteins (CD2, CD4, CD5, CD6, CD8) and PTK ZAP-70 were in part localized in buoyant, lipid-rich, detergent-resistant membrane GPI-microdomains of the COS cells.
Endogenous GPI-microdomains of COS cells appear to be, in contrast to those present in leucocytes, essentially devoid of associated PTKs. Our results indicate that GPI-anchor is sufficient to target proteins to these membrane specializations even if expressed ectopically.
Moreover, the N-terminal double acylation of the PTK Lck appears to be functional also in COS cells and targets the enzyme to the membrane GPI-microdomains implicated in receptor signalling.