Deregulation of MYCN, LIN28B and LET7 in a Molecular Subtype of Aggressive High-Grade Serous Ovarian Cancers

Abstract

Molecular subtypes of serous ovarian cancer have been recently described. Using data from independent datasets including over 900 primary tumour samples, we show that deregulation of the Let-7 pathway is specifically associated with the C5 molecular subtype of serous ovarian cancer. DNA copy number and gene expression of HMGA2, alleles of Let-7, LIN28, LIN28B, MYC, MYCN, DICER1, and RNASEN were measured using microarray and quantitative reverse transcriptase PCR. Immunohistochemistry was performed on 127 samples using tissue microarrays and anti-HMGA2 antibodies. Fluorescence in situ hybridisation of bacterial artificial chromosomes hybridized to 239 ovarian tumours was used to measure translocation at the LIN28B locus. Short interfering RNA knockdown in ovarian cell lines was used to test the functionality of associations observed. Four molecular subtypes (C1, C2, C4, C5) of high-grade serous ovarian cancers were robustly represented in each dataset and showed similar pattern of patient survival. We found highly specific activation of a pathway involving MYCN, LIN28B, Let-7 and HMGA2 in the C5 molecular subtype defined by MYCN amplification and over-expression, over-expression of MYCN targets including the Let-7 repressor LIN28B, loss of Let-7 expression and HMGA2 amplification and over-expression. DICER1, a known Let-7 target, and RNASEN were over-expressed in C5 tumours. We saw no evidence of translocation at the LIN28B locus in C5 tumours. The reported interaction between LIN28B and Let-7 was recapitulated by siRNA knockdown in ovarian cancer cell lines. Our results associate deregulation of MYCN and downstream targets, including Let-7 and oncofetal genes, with serous ovarian cancer. We define for the first time how elements of an oncogenic pathway, involving multiple genes that contribute to stem cell renewal, is specifically altered in a molecular subtype of serous ovarian cancer. By defining the drivers of a molecular subtype of serous ovarian cancers we provide a novel strategy for targeted therapeutic intervention.

Lin-28 Homologue A (LIN28A) Promotes Cell Cycle Progression via Regulation of Cyclin-dependent Kinase 2 (CDK2), Cyclin D1 (CCND1), and Cell Division Cycle 25 Homolog A (CDC25A) Expression in Cancer

“…In fact, we have previously identified four LIN28A regulatory miRNAs that were globally down-regulated in human tumors (67). In addition, overexpression of LIN28 activators, such as the Myc oncogene (47,54,68), may serve as another mechanism to deregulate LIN28A expression in epithelial tumors.…”

“…It has been reported that both expression of LIN28A and LIN28B are reac- (4,(42)(43)(44)(45)(46)(47). However, the expression and distribution of LIN28A in different types of epithelial tumors is still unknown.…”

“…Importantly, the expression of LIN28A/LIN28B is highly restricted to ES cells and developing tissues, and expression dramatically decreases as differentiation progresses (2,3,7,8,11,21,40,41). In human tumors, LIN28A/LIN28B expression is up-regulated/reactivated (4,(42)(43)(44)(45)(46)(47)(48)(49)(50)(51) and may function as an oncogene promoting malignant transformation (42,43,52,53), inducing metastasis (43,46,(52)(53)(54), regulating inflammation (5,43), and maintaining the cancer stem cells (43,45,(55)(56)(57). Clinical studies have indicated that higher levels of LIN28A/LIN28B expression are associated with poor clinical outcomes (44,58,59) and that LIN28 family polymorphisms may influence susceptibility to ovarian (60) and breast (61) cancers.…”

An in-tumor genetic screen reveals that the BET bromodomain protein, BRD4, is a potential therapeutic target in ovarian carcinoma

“…Expression profiling of large cohorts of HGSOC tumors have pointed to the existence of four distinct molecular subtypes (3,31), which collectively exhibit diverse pathological and clinical features (3,31,32). Notably, a molecular HGSOC subset, i.e., C5, has been defined by high level MYCN expression, which correlates with poor prognosis (32).…”

LIN-28B/let-7a/IGF-II axis molecular subtypes are associated with epithelial ovarian cancer prognosis

“…The involvement of the LIN-28B/let-7 axis in cancer has also been studied in vivo neuroblastoma animal model; LIN-28B overexpression-induced neuroblastma had markedly low levels of let-7 miRNA and high levels of MYC protein [13]. Frequent dysregulation of LIN-28B in human cancers including liver, breast, and ovary suggests that LIN-28B functions as an oncogene [2,6,11,14,15], influencing disease prognosis and patient response to treatment [5].…”