PIP2 is downregulated with ARF6 knockdown in culture cells.
The synthetic pathways of ceramide are two pathway.
First is the way SMase produces ceramide from SM.
Second is de nove pathway by SMS.
Acidic SMnase KO mice have a resistance for apoptosis.
Acidic SMase is localized in lysosome.
Abnormal acumulation of SM induced by delation of acidic SMase leads to Niemanpick A and B disease.
Which SM is gonna be cut by acidic SMase?
As you know, acidic SMase is localized in lysosome.
However, vesicle is released in some condition. So there is a possiblity that SMase is release to out of cell and cut the SM on the plasma membrane.
Sphingomyelin synthase (SMS)
There are two isoforms about SMS including SMS1 and SMS2.
SMS1 is mainly localized in Gogi apparatus.
SMS2 is localized at the plasma membrane.
Roles of SMS2 is controversial.
The generation os SM at the PM by the overexpression of SMS2 in CHO cells was reported to enhance TNF-alpha-induced apoptosis; it was suggested that SM generation in lipid rafts may increase the exposure of the TNF-R at the surface. Thus the level of SM at the PM and specifically in raft microdomains seems to regulate these events by modulating the cell surface expression of receptors.
On the other hand, SMS downregulation with siRNA potentiated cell death in Jurkat cells. potentially through increasing ceramide levels.
This paper is very important for me.
They use D609 and PC-PLC antibody and stain PC-PLC on the plasma membrane!
U73122 is a potent inhibitor for PIP2-specific phospholipase C.
The mechanism by which U73122 inhibits this enzyme is unclear.
6microM U73122 almost completely blocks increase in Ca++ in response to ATP in fibroblast.
10microM U73122 partialy blocks increase in Ca++ in response to ATP in MG6-1 cells. Incubation time is only 3min!