Solute exchange through gap junctions lessens the adverse effects of inactivating mutations in metabolite-handling genes

Elife. 2022 Sep 15:11:e78425. doi: 10.7554/eLife.78425.

Abstract

Growth of cancer cells in vitro can be attenuated by genetically inactivating selected metabolic pathways. However, loss-of-function mutations in metabolic pathways are not negatively selected in human cancers, indicating that these genes are not essential in vivo. We hypothesize that spontaneous mutations in 'metabolic genes' will not necessarily produce functional defects because mutation-bearing cells may be rescued by metabolite exchange with neighboring wild-type cells via gap junctions. Using fluorescent substances to probe intercellular diffusion, we show that colorectal cancer (CRC) cells are coupled by gap junctions assembled from connexins, particularly Cx26. Cells with genetically inactivated components of pH regulation (SLC9A1), glycolysis (ALDOA), or mitochondrial respiration (NDUFS1) could be rescued through access to functional proteins in co-cultured wild-type cells. The effect of diffusive coupling was also observed in co-culture xenografts. Rescue was largely dependent on solute exchange via Cx26 channels, a uniformly and constitutively expressed isoform in CRCs. Due to diffusive coupling, the emergent phenotype is less heterogenous than its genotype, and thus an individual cell should not be considered as the unit under selection, at least for metabolite-handling processes. Our findings can explain why certain loss-of-function mutations in genes ascribed as 'essential' do not influence the growth of human cancers.

Keywords: biochemistry; cancer biology; cell lines; chemical biology; colorectal cancer; knockout cells; selection.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Connexin 26 / genetics
  • Connexin 26 / metabolism
  • Connexins* / genetics
  • Connexins* / metabolism
  • Gap Junctions* / metabolism
  • Humans
  • Mutation
  • Phenotype
  • Protein Isoforms / metabolism

Substances

  • Connexins
  • Protein Isoforms
  • Connexin 26

Associated data

  • GEO/GSE116222

Grants and funding

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.