Abstract 554: Differential response to retinoid treatment of normal and transformed murine mammary cells overexpressing protein kinase C (PKC) isoforms.
Authors: Díaz Bessone María I. , Berardi Damian E. , Cirigliano Stefano M. , Flumian Carolina , Bal de Kier Joffe Elisa D. , Todaro Laura B. , Urtreger Alejandro J. 
Published: August 2014

Some of the most promising signaling pathways for breast cancer treatment include the PKC family, involved in proliferation and apoptosis, and the retinoid system mainly involved in differentiation.

In this work we have overexpressed α or δ PKC isoforms in two murine mammary models, a tumor-derived cell line (LM3) and a normal mammary gland-derived line (NMuMG), in order to analyze whether elevated expression of these kinases alter the sensitivity to retinoid treatment.

The overexpression of α or δ PKC isozymes did not induce detectable morphological alterations either in LM3 or in NMuMG cell lines. In the transformed cell context, the overexpression of PKCα increased cell proliferation (population doubling time: 14.8±2.3 h vs 21.2±3.1 h in control cells p&lt;0.05) and motility (wound coverage: 69.3±8.3% vs 41.2±5.1% in control cells p&lt;0.05), alterations that could be associated with an aggressive in vivo tumor behavior. Interestingly, at the same time, PKCα sensitized LM3 cells to the effects of the All-Trans-Retinoic Acid (ATRA) as evidenced by a significant reduction in both parameters.

On the contrary, PKCδ overexpression did not affect either LM3 cells in vitro behavior or their response to ATRA. However, through a RARE-luciferase gene reporter assay, we could determine that the overexpression of PKCδ increased the activity of the retinoic acid receptors.

In the normal cell context (NMuMG cells), the overexpression of both PKCs did not induce alterations in the proliferative potential (population doubling time: 14.8±0.8 h) or cell motility (wound coverage: 37.8±1.6%). Moreover, the subsequent treatment with ATRA neither affected the above mentioned parameters.

Upon othotopic inoculation into syngeneic mice, LM3-PKCα cells formed tumors with higher growth rate and metastatic potential than LM3-vector ones. In vivo treatment with a subcutaneous ATRA pellet reduced both the local tumor growth and the number of spontaneous lung metastases (Md [Range]: 9 [0-27] vs 55 [20-75] for LM3-PKCα treated or not respectively p&lt;0.05). PKCδ overexpression did not affect in vivo LM3 behavior.

Our results show that in an already transformed context, PKCα overexpression induced a more aggressive phenotype but also conferred sensitivity to the retinoid treatment. On the other side high PKCδ levels increased the activity of retinoid receptors but did not modulate biological cell responses to this compound. In a normal cell context, both PKC isoforms as well as the retinoid treatment are innocuous thus ensuring the safeness use of retinoids in patients with aggressive breast tumors associated with high PKCα expression.

Citation Format: María I. Díaz Bessone, Damian E. Berardi, Stefano M. Cirigliano, Carolina Flumian, Elisa D. Bal de Kier Joffe, Laura B. Todaro, Alejandro J. Urtreger. Differential response to retinoid treatment of normal and transformed murine mammary cells overexpressing protein kinase C (PKC) isoforms. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 554. doi:10.1158/1538-7445.AM2013-554