HPV16 E5 affects the KGFR/FGFR2b-mediated epithelial growth through alteration of the receptor expression, signaling and endocytic traffic

Abstract

The E5 oncoprotein of the human papillomavirus type 16 (HPV16 E5) cooperates in cervical carcinogenesis and in epithelial transformation deregulating cell growth, survival and differentiation through the modulation of growth factor receptors. Among the epithelial receptor tyrosine kinases, the keratinocyte growth factor receptor/ fibroblast growth factor receptor 2b (KGFR/FGFR2b) is a major paracrine mediator of epithelial homeostasis and appears to have an unique and unusual role in epithelial tissues, exerting a tumor-suppressive function in vitro and in vivo. With the aim to better elucidate the molecular events involved in the pathological activity of 16E5, we investigated if the viral protein would be able to affect the KGFR expression, signaling and turnover by interference with its degradative and recycling endocytic pathways. Quantitative reverse transcriptase-PCR and biochemical approaches on human keratinocytes transfected with 16E5-HA showed that E5 protein is able to induce KGFR down-modulation at both transcript and protein levels. Immunofluorescence microscopy in double-transfected cells expressing both E5 and KGFR revealed that the viral protein alters the receptor endocytic trafficking and triggers its endosomal sorting to the indirect juxtanuclear recycling pathway. The shift from lysosomal degradation to recycling at the plasma membrane correlates with a reduced phosphorylation of the fibroblast growth factor receptor substrate-2a tyrosine 196, the major docking site for Grb2-Cbl complexes responsible for receptor ubiquitination and degradation. 5 0 -Bromo-deoxyuridine incorporation assay demonstrated that expression of 16E5 induces a decrease in the growth response to the receptor ligands as a consequence of KGFR down-modulation, suggesting that 16E5 might have a role on HPV infection in perturbing the KGFR-mediated physiological behavior of confluent keratinocytes committed to differentiation.

MALAT1-miR-124-RBG2 axis is involved in growth and invasion of HR-HPV-positive cervical cancer cells

“…Growth factor receptor-bound protein 2 also known as GRB2 is an adaptor protein involved in signal transduction/cell communication [25]. HPV-16 infection is a cause of significantly increased GRB2 expression in cervical cancer, of which is involved in enhanced EGFR internalization and mTORC1 activation [26] and KGFR/FGFR2b-mediated epithelial growth [27]. In the present study, we verified a direct interaction between miR-124 and 3′UTR of GRB2.…”

Human Papillomavirus Infections: Warts or Cancer?

“…LRR sequences and the MAPK docking motifs are conserved among human and animal PVs. In light of the crucial role of MAP kinases, the ability of the HPV E5 protein to enhance signal transduction from receptor tyrosine kinases (Pedroza-Saavedra et al 2010;Suprynowicz et al 2010;Belleudi et al 2011) that function upstream of MEK1/2 and ERK1/2 would predict that it plays an important role in viral DNA amplification, and indeed it does in organotypic cultures (J-H Yu, TR Broker, and LT Chow, unpubl. ).…”

HPV Infections: Basis of Neoplastic Transformation and Related Molecular Tests

“…Although the main transforming activity belongs to the E6 and E7 proteins, the E5 protein can enhance their functions contributing to tumor progression, and if expressed alone exhibit a weak transforming potential; moreover E5 contributes to the immuno-escape mechanisms and in the pathway of the growth-factor receptors such as the EGFR and KGFR [14][15].…”