Abstract:

The secretory pathway is essential for eukaryotic life. Proteins in the secretory pathway bud off the Golgi apparatus in post-Golgi carriers which traffic to the plasma membrane. We have performed biochemical purification and mass spectrometry of the carriers to characterise their contents. We have subsequently performed a CRISPR-KO screen to identify novel components of the secretory pathway. We characterise the protein PTPN23 as a novel component of the secretory pathway. Interestingly, we also identify several subunits of the exocyst complex. Depletion of all canonical exocyst subunits causes cargo accumulation in post-Golgi carriers. Exocyst subunits are recruited to and co-localise with carriers. Exocyst abrogation followed by kinetic trafficking assays of soluble cargoes results in intracellular cargo accumulation. Unbiased secretomics reveals impairment of soluble protein secretion after exocyst subunit knock-out. Importantly, in specialised cell types, the loss of exocyst prevents constitutive secretion of antibodies in lymphocytes and of leptin in adipocytes. These data identify exocyst as the functional tether of secretory post-Golgi carriers at the plasma membrane and an essential component of the mammalian constitutive secretory pathway.

 

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