Stefan CJ, Padilla SM, Audhya A, Emr SD

The Saccharomyces cerevisiae synaptojanin-like proteins (Sjl1, Sjl2, and Sjl3) are phosphoinositide (PI) phosphatases that regulate PI metabolism in the control of actin organization and membrane trafficking. However, the primary sites of action for each of the yeast synaptojanin-like proteins remain unclear. In this study, we show that Sjl2 is localized ...

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to cortical actin patches, sites of endocytosis. Cortical recruitment of Sjl2 requires the actin patch component Abp1. Consistent with this, the SH3 domain-containing protein Abp1 physically associates with Sjl2 through its proline-rich domain. Furthermore, abp1Delta mutations confer defects resembling loss of SJL2; sjl1Delta abp1Delta double-mutant cells exhibit invaginated plasma membranes and impaired endocytosis, findings similar to those for sjl1Delta sjl2Delta mutant cells. Thus, Abp1 acts as an adaptor protein in the localization or concentration of Sjl2 during late stages of endocytic vesicle formation. Overexpression of the Hip1-related protein Sla2 delayed the formation of extended plasma membrane invaginations in sjl2ts cells, indicating that Sla2 may become limiting or misregulated in cells with impaired PI phosphatase activity. Consistent with this, the cortical actin patch protein Sla2 is mislocalized in sjl1Delta sjl2Delta mutant cells. Together, our studies suggest that PI metabolism by the synaptojanin-like proteins coordinately directs actin dynamics and membrane invagination, in part by regulation of Sla2.

Date: Apr. 01, 2005

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