JAK2/STAT and LKB1: An Interaction Linking PRL-Mediated Metabolic Changes and Structural Integrity in MDA-MB-231 Human Breast Cancer Cells

Abstract

Janus-activated kinase 2 (JAK2)/Signal transducer and activator of transcription (STAT) signaling is activated by prolactin (PRL) in breast cells and tissue. We have shown previously that PRL affects cellular metabolism in a human breast cancer cell type-dependent manner through differential activation of the Adenosine 5’-monophosphate-activated protein kinase (AMPK) energy sensing pathway, a response mediated by Liver kinase B1 (LKB1). LKB1 regulates diverse cellular processes, including metabolism and polarity. We have demonstrated that PRL regulates the expression of LKB1 through STAT proteins in the triple-negative, mesenchymal-like, aggressive MDA-MB-231 breast cancer cell line, and that knock-down of LKB1 dramatically alters the morphology of these cells. In ongoing research, we have established a novel interaction between JAK2 and LKB1. The association between these two proteins is blocked by treating cells with (E)-3(6-bromopyridin-2-yl)-2-cyano-N-((S0-1-phenylethyl)acrylamide) (WP1066), an analogue of AG490 that efficiently degrades JAK2. We have also evaluated whether inhibiting sustained PRL signaling through JAK2 affects LKB1-AMPK pathway activation. PRL-induced activation of LKB1, AMPK, and tuberous sclerosis complex 2 (TSC2), and inactivation of acetyl CoA carboxylase (ACC), were abrogated by WP1066 pre-treatment of MDA-MB-231 cells. In contrast, culture of MCF-7 cells in the presence of PRL resulted in sustained phoshorylation of AKT, which is known to block AMPK signaling by directly inactivating TSC2. AKT activation in this particular cell line is likely to be uncoupled from JAK2. As further read-out of the changes induced by blocking JAK2, phosphorylation/activation of STAT3 and STAT5 were also differentially affected by WP1066 pre-treatment in 184B5, MCF-7, and MDA-MB-231 cells. The association between JAK2 and LKB1, the metabolic effects linked to JAK2/LKB1-mediated signaling elicited by PRL in MDA-MB-231 cells, and interplay between several important intracellular signaling networks that regulate both metabolism and cell polarity merit further investigation in an extended panel of cells, as well as patient-derived samples. Our findings are of relevance in gaining a better understanding of the epithelial-to-mesenchymal transition (EMT) and mechanisms that protect aggressive cancer cells, allowing them to adapt to a changing microenvironment during disease progression, which may depend on extracellular cues that are spatio-temportally present.