Expression of neuropeptide calcitonin (CT) and its receptor (CTR) is frequently elevated in prostate cancers (PCs) and activation of CT–CTR axis in non-invasive PC cells induces an invasive phenotype. Specific, cell-permeable inhibitors of protein kinase A abolish CTR-stimulated invasion of PC cells. Since PKA is ubiquitously distributed in cells, the present study examined the mechanism(s) by which CTR-stimulated PKA activity is regulated in time and space. CT reduced cell adhesion but increased invasion of PC cells. Both these actions were abolished by st-Ht31 inhibitory peptide suggesting the involvement of an A-kinase anchoring protein (AKAP) in CT action. Next, we identified the AKAP associated with CT action by the subtraction of potential AKAP candidates using siRNAs. Knock-down of membrane-associated AKAP2, but not other AKAPs, abolished CT-stimulated invasion. Stable knock-down of AKAP2 in PC3-CTR cells remarkably decreased their cell proliferation, invasion, clonogenicity and ability to form orthotopic tumors and distant metastases in nude mice. Re-expression of AKAP2-wt restored these characteristics. Primary PC specimens displayed remarkable upregulation of CTR/AKAP2 expression as compared to benign prostates. Metastatic cancers displayed significantly higher CTR/AKAP2 expression than localized cancers. These results for the first time demonstrate that AKAP2 is expressed in human prostates, its expression is elevated in metastatic prostate cancer, and the knock-down of its expression remarkably decreased tumorigenicity and metastatic ability of prostate cancer cells. AKAP2 may serve as a critical component of CTR-mediated oncogenic actions.
Arvind Thakkar, Ahmed Aljameeli, Shibu Thomas and Girish V Shah
Afaf Aldahish, Ajay Kale, Ahmed Aljameeli and Girish V Shah
Stem cell-like-cancer cells are key drivers of tumor growth, metastasis, and relapse of cancer following remission. Prostate stem cell-like cancer cells isolated from human prostate cancer (PC) biopsies express CD44+/α2β1 hi/CD133+ cell surface markers and can self-renew in vitro. Expression of calcitonin (CT) and its receptor (CTR) is frequently elevated in PCs and activation of CT-CTR axis in non-invasive PC cells induces an invasive phenotype. We investigated whether CT-CTR autocrine axis induces stem cell-like phenotype in two PC cell lines. CT-CTR axis in these cell lines was activated by enforced expression of CTR. The cells were then examined for the changes in the expression of CD44 and CD133, collagen adherence, tumorigenic, metastatic and repopulating characteristics. The activation of CT-CTR axis led to a large increase in adherence to collagen and a remarkable increase of CD44 and CD133 in PC-3 and LNCaP cells. This was accompanied by a strong increase in tumorigenic, metastatic and repopulation properties of PC cells. However, the mutation of CTR-C PDZ-binding site in CTR almost abolished CTR-mediated increases in stem cell-like characteristics of PC cells. These results support an important role for CT-CTR axis in the progression of PC from localized cancer to an aggressive form, and a majority of proinvasive CTR actions may be mediated through its interaction with its partner protein at the PDZ-binding site. These results suggest that CT/CTR can serve as a valuable target to prevent the generation of stem-like PC cells.