Fig. 6

Model of PTHrP domain-specific actions in breast cancer progression and bone colonization. In the primary breast site (top left panel, left of arrows), PTHrP lacking the NLS and C-terminal domain decreases tumor cell proliferation through p27 induction driven by the tumor suppressor leukemia inhibitory factor receptor (LIFR). PTHrP lacking the NLS and C-terminal domain also preferentially induces p38 phosphorylation and signaling to inhibit cell cycling downstream of LIFR activation. In the breast, truncated PTHrP lacking the NLS alone (top left panel, right of arrows) downregulates LIFR expression (denoted by transparent coloring) and prevents induction of p27 expression and activation of p38 signaling (denoted by dashed arrows, dotted outlines and transparent coloring) to drive cell proliferation and tumor growth. In bone disseminated tumor cells (bottom panel), LIFR expression is downregulated and the induction of p27 by PTHrP lacking the NLS and C-terminal domain persists, but is not sufficient to repress metastatic outgrowth (denoted by dashed inhibitor line), in contrast to the primary tumor. In the bone, tumor cells expressing PTHrP peptides lacking the NLS or NLS and C-terminal domain readily proliferate into metastatic tumors. Image created with Biorender.com