Carroll, R. | bioRxiv Science

bioRxiv2018

Adaptor protein Bbc1 regulates localization of Wsp1 and Vrp1 during endocytic actin patch assembly

Arp2/3 complex-nucleated branched actin networks provide the force necessary for endocytosis. The Arp2/3 complex is activated by Nucleation Promoting Factors (NPFs) including the Schizosaccharomyces pombe proteins WASp Wsp1 and myosin-1 Myo1. There are >40 known yeast endocytic proteins with distinct spatial and temporal localizations and functions; however, it is still unclear how these proteins work together to drive endocytosis. We used quantitative live cell imaging to determine the function of the uncharacterized S. pombe protein Bbc1. We discovered Myo1 interacts with and recruits Bbc1 to sites of endocytosis. Bbc1 competes with verprolin Vrp1 for Myo1 binding, thus releasing Vrp1 and its binding partner Wsp1 from Myo1. Normally Myo1 remains at the base of the endocytic invagination and Vrp1-Wsp1 internalize with the endocytic vesicle; however, in the absence of Bbc1, a portion of Vrp1-Wsp1 remains with Myo1 at the base of the invagination and endocytic invaginations are twice as long. We propose that Bbc1 disrupts a transient Myo1-Vrp1-Wsp1 interaction and limits Arp2/3 complex-nucleation of actin branches at the plasma membrane.

cell biology↗

bioRxiv2017

Recurrent loss of heterozygosity correlates with clinical outcome in pancreatic neuroendocrine cancer

Pancreatic neuroendocrine tumors (pNETs) are uncommon cancers arising from pancreatic islet cells. Analysis of gene mutation, copy number and RNA expression of 57 sporadic pNETs showed that pNET genomes are dominated by aneuploidy. Remarkably, ~25% of pNETs had genomes characterized by recurrent loss of heterozygosity (LoH) of the same 10 chromosomes, accompanied by bi-allelic MEN1 inactivation, and these cases had generally poor clinical outcome. Another ~25% of all pNETs had chromosome 11 LoH and bi-allelic MEN1 inactivation, lacking the recurrent LoH pattern - these had universally good clinical outcome. Some level of aneuploidy was common, and overall ~80% of pNETs had LoH of [≥]1 chromosome. This aneuploidy led to changes in RNA expression at the level of whole chromosomes and allowed pathogenic germline variants (e.g. ATM) to be expressed unopposed, inactivating downstream tumor suppressor pathways. Some pNETs appear to utilize VHL gene methylation or mutation to activate pseudo-hypoxia. Contrary to expectation neither tumor morphology within well-differentiated pNETs nor single gene mutation had significant associations with clinical outcome, nor did expression of RNAs reflecting the activity of immune, differentiation, proliferative or tumor suppressor pathways. MEN1 was the only statistically significant recurrently mutated driver gene in pNETs. Only one pNET had clearly oncogenic and actionable SNVs (in PTEN and FLCN) confirmed by corroborating RNA expression changes. The two distinct patterns of aneuploidy described here, associated with markedly poor and good clinical outcome respectively, define a novel oncogenic mechanism and the first route to genomic precision oncology for this tumor type.

cancer biology↗