Modulation of RAB5A early endosome trafficking in response to KRas mediated macropinocytic fluxes in pancreatic cancer cells


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Christian Teske1,Christine Schweitzer1,Andrea Palamidessi2,Daniela Aust3,Giorgio Scita2,J├╝rgen Weitz1,Thilo Welsch1
1University Hospital Dresden, Dept. of Visceral, Thoracic and Vascular Surgery,2Fondazione Istituto FIRC di Oncologia Molecolare (IFOM),3University Hospital Dresden, Dept. of Pathology

Abstract

Background

KRAS is the key mutated gene in pancreatic ductal adenocarcinoma (PDAC). Emerging evidence indicates that KRas modulates endocytic uptake to enhance nutrient supply and cancer growth. The present study aimed to explore the fate of early endosomal trafficking under the control of KRas expression in PDAC.

Method

PDAC cell lines were treated with siRNA for specific knockdown of KRas and examined for early and late endosomal markers using immunofluorescence analysis. Functional assays for endosome degradation with DQ-BSA and the inhibitors chloroquine (CQ) and bafilomycin A1 were performed. 

Results

PANC-1 cells lacking KRas exhibited significantly enlarged early and late endosomes containing internalized dextran and epidermal growth factor. Endosome enlargement was accompanied by reduced endosomal degradation. Both KRas silencing and lysosomal blockade caused an upregulation of the master regulator of early endosome biogenesis, RAB5A, which is likely responsible for the expansion of the early endosomal compartment. Simultaneous KRAS/RAB5A knockdown abolished endosomal enlargement. In contrast, early endosome shrinkage was seen in MIA PaCa-2 cells despite RAB5A upregulation, indicating that distinct KRas-modulated responses operate in different metabolic subtypes of PDAC.

Conclusion

In conclusion, mutant KRAS promotes endosomal degradation in PDAC cell lines, which is impaired by KRAS silencing. Moreover, KRAS silencing activates RAB5A upregulation and drives PDAC subtype-dependent modulation of endosome trafficking.