The C-terminal region of PTHrP, in addition to the nuclear localization signal, is essential for the intracrine stimulation of proliferation in vascular smooth muscle cells

PTHrP is secreted by most cell types. In addition to a paracrine/autocrine role, PTHrP has "intracrine" actions, entering the nuclear compartment unde r the direction of a classic bipartite nuclear localization signal. In vasc ular smooth muscle cells, nuclear entry stimulates mitogenesis. In the curr ent study, we sought to more precisely define the regions of PTHrP required for the activation of mitogenesis in vascular smooth muscle cells. PTHrP d eletion mutants missing large regions [i.e. the signal peptide, N terminus (1-36), mid region (38-86), nuclear localization signal, C terminus (108-13 9), or combinations of the above] were expressed in A-10 vascular smooth mu scle cells. The consequences on nuclear localization and proliferation were examined. Deletion of the nuclear localization signal prevented nuclear en try and slowed proliferation. Deletion of the highly conserved N terminus o r mid region had no impact on nuclear localization or on proliferation. Del etion of the C terminus had no deleterious effect on nuclear localization b ut dramatically reduced proliferation. Thus, the nuclear localization signa l is both necessary and sufficient for nuclear localization of PTHrP. In co ntrast, activation of proliferation in vascular smooth muscle cells require s both an intact nuclear localization signal and an intact C terminus. Wher eas the nuclear localization signal is required for nuclear entry, the C te rminus may serve a transactivating function to stimulate mitogenesis once i nside the nucleus of vascular smooth muscle cells.