Phafin2 modulates the structure and function of endosomes by a Rab5-dependent mechanism.
By regulating the amount of protein receptors on the cell membrane and the metabolisms of receptor-bound ligands, endocytosis represents one of the fundamental biological activities that regulate how cells respond to the environment. We report here that a Fab1-YotB-Vac1p-EEA1 (FYVE) domain-containing lipid associated protein, called Phafin2, is preferentially expressed in the human hepatocellular carcinoma (HCC) and is involved in the biogenesis of endosomes. Over-expression of Phafin2 or its FYVE domain results in the formation of enlarged endosomes that are still functional for endocytosis; the biogenesis of such abnormal organelles is mediated by phosphoinositide 3-kinases (PI3K) and Rab5 signaling. Using fluorescence resonance energy transfer measured by fluorescence lifetime imaging microscopy (FLIM-FRET), we further demonstrate in live cells that Phafin2 can directly activate Rab5. By modulating the receptor internalization/recycling and Rab5 activation, Phafin2 affects the density of membranous insulin receptors, and regulates the transcriptional activity of AP-1 that is downstream of the insulin signaling pathway. These results provide a vivid example that an endosome modulator, such as Phafin2, may control the cells' responses to the extracellular cues.
Lin
Wen-Jie
WJ
Institute of Microbiology and Immunology, National Yang-Ming University, Taipei, Taiwan.
Yang
Chih-Yung
CY
Lin
Ying-Chih
YC
Tsai
Meng-Chun
MC
Yang
Chu-Wen
CW
Tung
Chien-Yi
CY
Ho
Pei-Yun
PY
Kao
Fu-Jen
FJ
Lin
Chi-Hung
CH
D045744:Cell Line, Tumor; D011992:Endosomes / Q000378:metabolism* / Q000648:ultrastructure; D006801:Humans; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011972:Receptor, Insulin / Q000378:metabolism; D015398:Signal Transduction; D018808:Transcription Factor AP-1 / Q000378:metabolism; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism*; D020696:rab5 GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
D019869:Phosphatidylinositol 3-Kinases; D011972:Receptor, Insulin; D018808:Transcription Factor AP-1; D033921:Vesicular Transport Proteins; D020696:rab5 GTP-Binding Proteins; C547687:PLEKHF2 protein, human