Biochemical and genetic analysis of the adaptor protein SH3P7 : insights from a newly generated knockout mouse
SH3P7 (mAbp1/Hip55) is a widely expressed actin-binding adaptor protein identified as a substrate for protein tyrosine kinase (PTK) after BCR activation. In addition to two protein-binding modules specific for filamentous actin, SH3P7 also contains an SH3 domain. The biochemical studies presented here, show that SH3P7 interacts via this domain with key components of endocytosis in B cells. SH3P7 binding to Hip1R, a huntingtin family member and new component of clathrin-coated vesicles, is characterized in greater detail. In resting B cells, Hip1R is constitutively bound to SH3P7. Stimulation of B cells with BCR-crosslinking-antibody or pervanadate-treatment, abolishes the interaction in a time-dependent manner. Thus the SH3P7/Hip1R interaction might be a structural link between BCR activation, the actin-cytoskeleton and endocytosis. To inactivate the mouse sh3p7 gene, the gene was first cloned and characterized. This allowed the construction of a deletion vector, which was used to target the sh3p7 gene in embryonic stem cells. Sh3p7-/- mice were successfully produced and are viable and fertile. Initial experiments with sh3p7-/- B cells indicate a role of SH3P7 as inhibitor of BCR internalization. Male sh3p7-/- and sh3p7+/- mice of this strain develop splenomegaly and a progressive and ultimately fatal disease at 3-4 months of age. Initial FACS-analysis of the cellular composition of the spleen show drastic reduction of T1 B cells which might be interpreted as defect in B cell development or maturation. Symptoms such as progressive paralysis implicate a neuronal disease in male sh3p7-/- and sh3p7+/- mice. Future detailed studies of the sh3p7 knockout might give insight into related human diseases. In summary provides this work evidence for a function of SH3P7 in BCR endocytosis and shows the result of the generation and initial analysis of a new knockout mouse.
SH3P7, Hip1R, Clathrin-vermittelte Endocytose, BCR Internalisierung, BCR internalisation, clathrin-mediated endocytosis
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