YIP1 family member 4 (YIPF4) is a novel cellular binding partner of the papillomavirus E5 proteins

Papillomaviruses (PVs) are capable of causing a broad spectrum of diseases with the human PVs (HPVs) being responsible for a great portion of cervical, anogenital and head and neck cancers worldwide. The PV oncoprotein E5 plays roles in host cell transformation, the PV life-cycle and viral immune evasion. However, the mechanisms by which E5 achieves this are unclear. A yeast two-hybrid screen identified a novel Golgi protein, YIPF4, as a potential interactor of 16E5. YIPF4 is a member of the integral membrane protein family YIP1 that is thought to mediate intracellular trafficking. Quantitative polymerase chain reaction, Western blot and immuno-histochemistry analysis confirmed that YIPF4 is expressed in host cells of HPV infection in cell culture systems and in clinical samples of HPV16 induced cervical lesions. This implies that YIPF4 could be a relevant in vivo binding partner of E5. Upon the differentiation of HPV18 positive keratinoctyes in semisolid medium, the YIPF4 expression levels were stabilised compared to control cells suggesting that YIPF4 might play a role during the productive viral life-cycle. A differential, detergent permeabilisation assay provided the first experimental evidence for a three trans-membrane domain model of YIPF4. Co-immuno-precipitation revealed a conserved interaction of YIPF4 with E5 proteins from clinically important PVs indicating a potentially invaluable role of this complex for the virus. A flow cytometry approach unexpectedly revealed that neither E5 nor YIPF4 proteins modulate the trafficking of human leukocyte antigen class I molecules to facilitate viral immune evasion. A preliminary cellular interactome of YIPF4 was determined in a label free mass spectrometry experiment to facilitate the search for the function of the highly conserved E5/YIPF4 protein complex. This knowledge might contribute to elucidating new targets for the development of therapeutic agents against the broad spectrum of PV associated diseases.