Endocytosis is a barrier to reprogramming

Using a combination of gene network analysis and gene ontology analysis we identified key regulators of the endocytic pathway among the top 5% significance level (p=0.0502) TRA-1-81+ screen hits. Receptor mediated endocytosis is frequently initiated by ubiquitination of the receptor and/or proximal surface proteins. Screen hits MARCH3 (p=0.0152), RNF40 (p=0.0044), and NEDD4 (p=0.0172) have all been shown to mediate receptor ubiquitination and subsequent targeting for endocytosis [1-5]. Once targeted, transport vesicle formation requires RABEP1 (p=0.0262) and EHD2 (p=0.0262) which are screen hits [6-7]. Early endosome formation involves formation of coated pits comprised of clathrin (CLTA p=0.0046) as well as WDFY1 (p=0.0222) [8], both top screen hits. Multiple screen hits were identified as vesicle surface proteins mediating late endosome-lysosome fusion (MCOLN1 p=0.0108, PIK3R4 p=0.023, VPS25 p=0.015, HSPA8 p=0.0242, SCARB2 p=0.014) [9-10]. Lysosomal lipases and proteases such as LIPA (p=0.0394), GM2A (p=0.035), and LGMN (p=0.0006) were screen hits as well as PIK3C3 (p=0.0166) which mediates lysosomal protein shuttling into the lysosome [11-13]. Lastly, the lysosomal protein SLC17A5 (p=0.0192) and DRAM1 (p=0.044), a lysosome surface membrane protein associated with autophagy, were also screen hits [14].

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