Blimp1 Activation by AP-1 in Human Lung Cancer Cells Promotes a Migratory Phenotype and Is Inhibited by the Lysyl Oxidase Propeptide

Abstract

B lymphocyte-induced maturation protein 1 (Blimp1) is a master regulator of B cell differentiation, and controls migration of primordial germ cells. Recently we observed aberrant Blimp1 expression in breast cancer cells resulting from an NF-κB RelB to Ras signaling pathway. In order to address the question of whether the unexpected expression of Blimp1 is seen in other epithelial-derived tumors, we selected lung cancers as they are frequently driven by Ras signaling. Blimp1 was detected in all five lung cancer cell lines examined and shown to promote lung cancer cell migration and invasion. Interrogation of microarray datasets demonstrated elevated BLIMP1 RNA expression in lung adenocarcinoma, pancreatic ductal carcinomas, head and neck tumors as well as in glioblastomas. Involvement of Ras and its downstream kinase c-Raf was confirmed using mutant and siRNA strategies. We next addressed the issue of mechanism of Blimp1 activation in lung cancer. Using knockdown and ectopic expression, the role of the Activator Protein (AP)-1 family of transcription factors was demonstrated. Further, chromatin immunoprecipitation assays confirmed binding to identified AP-1 elements in the BLIMP1 promoter of ectopically expressed c-Jun and of endogenous AP-1 subunits following serum stimulation. The propeptide domain of lysyl oxidase (LOX-PP) was identified as a tumor suppressor, with ability to reduce Ras signaling in lung cancer cells. LOX-PP reduced expression of Blimp1 by binding to c-Raf and inhibiting activation of AP-1, thereby attenuating the migratory phenotype of lung cancer cells. Thus, Blimp1 is a mediator of Ras/Raf/AP-1 signaling that promotes cell migration, and is repressed by LOX-PP in lung cancer.

BLIMP1 Induces Transient Metastatic Heterogeneity in Pancreatic Cancer

“…6L). Our results are consistent with the link between Blimp1 and migratory ability of human lung and breast cancer cell lines in vitro (73,74). Blimp1 has not been described as a hypoxia/Hif target gene in normal cell types but hypoxia may also influence Blimp1 expression in those settings.…”

UXT Is a LOX-PP Interacting Protein That Modulates Estrogen Receptor Alpha Activity in Breast Cancer Cells

“…Ectopic expression of LOX-PP reduced UXT protein levels by 40-50%. LOX-PP is a glycosylated protein that appears differentially modified in various cell types [Vora et al, 2010;Yu et al, 2012]. Consistently, ectopically expressed LOX-PP migrated at the expected position for unprocessed protein ($21 kDa) and also yielded multiple, glycosylated bands migrating more slowly, as seen previously.…”

“…In Ras ‐NIH 3T3 cells, expression of LOX‐PP, but not of the processed LOX enzyme, inhibited the transformed phenotype of the fibroblasts [Palamakumbura et al, ]. Similarly, ectopic PRO‐LOX or LOX‐PP expression in H1299 lung, PANC‐1 pancreatic and Her‐2/neu breast cancer cell lines reduced cell migration, growth in soft agar, invasive colony formation in Matrigel and the activation of extracellular signal‐regulated kinases (ERK) and Akt [Min et al, ; Wu et al, ; Yu et al, ]. Importantly, ectopic LOX‐PP expression or direct tumoral administration of recombinant protein reduced Her‐2‐driven breast tumor burden in a xenograft model [Min et al, ; Bais et al, ].…”

Dysregulation of Blimp1 transcriptional repressor unleashes p130Cas/ErbB2 breast cancer invasion

“…Indeed, it has been shown that the downmodulation of Blimp1 in solid tumors leads to impaired cell migration both in non-small cell lung cancer and in ERα positive breast cancer cell lines, where Blimp1 represses the BMP5 protein 16, 18 .…”