Somatic mutation of Afadin leads to anchorage independent survival and metastatic growth of breast cancer through αE-catenin dependent destabilization of the adherens junction

Abstract

ABSTRACTLoss of E-cadherin (CDH1) and the adherens junction (AJ) drive development and progression of invasive lobular breast cancer (ILC). However, approximately 40% retain wild typeCDH1alleles, indicating that modulation of other genes attenuates the AJ during ILC etiology. To identify alternative drivers, we performed targeted sequencing inCDH1wild type samples, based on a defined set of 100 AJ, tight junction, and desmosome genes we designated as the ‘Adhesome’. In 146 ILC samples, we identified 62 cases (43%) with wild typeCDH1alleles in which we detected a total of 284 mutations in 36 Adhesome genes. After selection based on occurrence and potential loss of function, we identified an inactivating frameshift mutation in Afadin (AFDN; p.Lys630fs).Functional studies in E-cadherin-expressing breast cancer cells showed that Afadin knockout leads to immature AJs, and a non-cohesive phenotype accompanied by actomyosin dependent anoikis resistance, which are classical ILC hallmarks. Afadin reconstitutions show that F-actin organization critically depends on the ⍰E-catenin binding CC domain. Afadin loss in intraductal xenograft mouse breast cancer models leads to ILC-type morphologies and overt lung metastases.AFDNtruncate reconstitutions revealed that deletion of the C-terminal ⍰E-catenin binding CC domain is sufficient to drive metastatic ILC. In conclusion, we identified and functionally coupled a somatic frameshiftAFDNmutation in breast cancer to destabilization the epithelial AJ and the development of ILC hallmarks such as actomyosin-dependent anoikis resistance and single cell invasion. As such, Afadin represents a candidate tumor suppressor for E-cadherin-positive ILC development and progression.