Loss of LKB1 and p53 synergizes to alter fallopian tube epithelial phenotype and high-grade serous tumorigenesis

Abstract

Liver kinase B1 (LKB1) is a tumor suppressor ubiquitously expressed serine/threonine protein kinase involved in energy metabolism and cellular polarity. In microarray experiments that compared normal tubal epithelium with high-grade serous carcinoma (HGSC), we observed a decrease in LKB1 mRNA expression in HGSC. In this study, we demonstrate that loss of cytoplasmic and nuclear LKB1 protein expression is frequently observed in tubal cancer precursor lesions as well as in both sporadic and hereditary HGSCs compared with other ovarian cancer histotypes. Bi-allelic genomic loss of LKB1 in HGSC did not account for the majority of cases with a decrease in protein expression. In vitro, shLKB1-fallopian tube epithelial (FTE) cells underwent premature cellular arrest and in ex vivo FTE culture, LKB1 loss and p53 mutant synergized to disrupt apical to basal polarity and decrease the number of ciliated cells. Overexpression of cyclin E1 allowed for bypass of LKB1-induced cellular arrest, and increased both proliferation and anchorage-independent growth of transformed FTE cells. These data suggest that LKB1 loss early in ovarian serous tumorigenesis has an integral role in tumor promotion by disrupting apical to basal polarity in the presence of mutated p53 in fallopian tube cells.

AMPK-independent LKB1 activity is required for efficient epithelial ovarian cancer metastasis

“…Since FT190 cells are immortalized by expression of SV40 large T antigen [30], our results also indicate that the combination of p53 and pRb inactivation with LKB1 loss is insufficient for malignant transformation of FTE cells. Given the report suggesting decreased LKB1 protein expression in pre-malignant STIC lesions and primary serous ovarian tumours [15], we propose that LKB1 re-expression and its pro-metastatic effects are manifest at later steps in ovarian tumorigenesis after initial neoplastic transformation.…”

LKB1 expression reverses the tumorigenicity of L02 cells

“…There is ample evidence that deregulation of the LKB1 signaling pathway appears to play a major role in tumor pathogenesis, since it facilitates malignant development through suppression of cell apoptosis and growth arrest (27)(28)(29)(30). To investigate the oncogenic state of the L02 cell line, functional assays were carried out including evaluation of the clonogenicity and tumor-initiating potential.…”

“…anchorage-independent growth in soft agar is one of the hallmark characteristics of cellular transformation and uncontrolled cell growth, with normal cells typically not capable of growth in semi-solid matrices (26). Recent studies have provided compelling evidence that loss of LKB1 activity is a critical step in oncogenesis (27)(28)(29)(30). To explore the oncogenic potential of LKB1-deficient L02 cells, a soft agar colony formation assay was carried out.…”

C/EBPδ demonstrates a dichotomous role in tumor initiation and promotion of epithelial carcinoma

“…To determine if C/EBPδ protein expression seen in HGSC is correlated to genomic changes, we used a cohort of HGSC genomic data (Affymetrix 6.0 SNP array) of chemotherapy naïve and stage III/IV cases (n=75) (Milea, George et al 2013, George, Milea et al 2015. Seventeen per cent (13/75) of cases (p<0.0001) had an amplification of the gene whereas only 2% (2/75) cases revealed a deletion; most cases (59/75) remained diploid at that genomic locus (Supplementary Figure 1A).…”

“…A pre-neoplastic lesion called the p53 signature is the earliest mutational and genomic event described in the gradual steps of HGSC development (Folkins, Jarboe et al 2008). The acquisition of somatic TP53 mutations is followed by additional genomic alterations, cellular tufting and loss of polarity, resulting in the development of neoplastic serous tubal intraepithelial carcinoma (STIC) (Shaw, Rouzbahman et al 2009, Sehdev, Kurman et al 2010, Jazaeri, Bryant et al 2011, Visvanathan, Vang et al 2011, George and Shaw 2014, George, Milea et al 2015. STIC lesions share multiple genomic copy number alterations, along with mutations in tumor suppressors and oncogenes, including TP53, BRCA1 and BRCA2,RB1,STK11,FOXO3a,CCNE1,STATHMIN1 and The fallopian tube epithelia (FTE) undergo monthly cycles of hormonally driven proliferation and differentiation.…”