P1.12-01 CD81-HOTTIP Regulating Loop Enhances Myc-Mediated Chemoresistance in Small Cell Lung Cancer via ERK Signaling Pathway

Abstract

The majority of small cell lung cancer (SCLC) patients who are treated with platinum-based chemotherapy will eventually develops into drug resistance. Currently, there are no effective durable therapies for patients with resistant recurrent SCLC. High expression of CD81 is associated with SCLC chemoresistance and poor clinical outcome. Here, our goal is to study the underlying mechanism and define a novel signaling pathway controlled by CD81 -modulating SCLC chemotherapy resistance. The expression of CD81, HOTTIP, and MYCBP were examined in human SCLC tissues, patient-derived xenograft (PDX) models, cell lines derived xenograft tumor model, and SCLC cell lines. The correlations between CD81 and HOTTIP were also confirmed by RNA immunoprecipitation and luciferase reporter assay. Functional analysis of HOTTIP, MYCBP, and ERK signaling was investigated in SCLC cell lines and xenografts. Knockdown CD81 enhanced cell responsiveness to chemotherapeutic drugs in SCLC and decreased the expression of HOTTIP, as well as inhibited the intra-nuclear translocation of MYCBP/MYC complex. Conversely, overexpression of CD81 decreased the chemotherapeutic reactivity and increased the expression of HOTTIP and promoting nuclear translocation of MYCBP/MYC complex. CD81 upregulation of HOTTIP requires the transcription factor TCF4. Further analysis demonstrated that CD81-mediated activation of ERK signaling pathway and inhibition of β-catenin degradation leads to promotion of β-catenin transfer to the nucleus. Nuclear β-catenin enhances transcriptional activity of TCF4 and then promotes the transcription of HOTTIP. Synergistically, HOTTIP could bind and increase the nucleus transduction of the MYCBP, form a HOTTIP/MYCBP/MYC complex in nucleus, resulting in increased MYC levels in nucleus. Nuclear MYC further mediates chemoresistance and promotes CD81 expression, forming a positive feedback regulatory pathway in SCLC. In addition, in vivo experiments showed that inhibitors that target the CD81-HOTTIP feedback regulatory loop combined with chemotherapeutic drugs can reverse the chemotherapeutic resistance of SCLC. Our findings suggest a novel feedback regulatory pathway dominated by CD81 and HOTTIP controlling SCLC chemotherapeutic resistance, which could serve as a new therapeutic targets for this devastating disease.