Physiopathology of the interstitial cells of the gut and gastrointestinal stromal tumors: morphological, functional, and molecular approaches.

Interstitial cells of Cajal (ICC) are involved in the control of gut motility. They present rhythmic variations of their membrane potential and form electrically coupled networks that assure the spatio-temporal organization of slow waves of depolarization, also called pacemaker component, of the gut smooth muscle. ICC are also involved in the transmission of the nerve input to the smooth muscle and play a role of mechanosensors.

The tyrosine kinase receptor (proto-oncogene) KIT is required for the development of ICC and KIT-immunoreactivity identifies ICC by immunohistochemistry. Alterations of ICC have been reported in several pathological conditions both in animal models and in human. Gastrointestinal stromal tumors (GIST) derive from ICC or their precursors and gain-of-function (oncogenic) mutations of KIT are encountered in a majority of GIST, for which tyrosine kinase inhibitors (TKI) epitomize the concept of targeted therapy.

Our main goals are, on one hand, to investigate the contribution of ICC and other types of interstitial cells to the pathophysiology of gastrointestinal motility in mouse models and human diseases and, on the other hand, to identify alterations of the gene expression profile and signal transduction pathways induced in ICC by KIT oncogenic mutants, in in-vitro and in-vivo models and in human GIST.

Our recent works have brought for the first time the phosphodiesterase 3A (PDE3A) into the spotlight in the field of ICC and GIST biology. 

PDE3A is a marker for ICC and is expressed in most human GIST. PDE3A is also an actor in ICC and GIST biology: PDE3A knock-out mice have a reduced amount of ICC. The PDE3 inhibitor cilostazol exerts strong cytotoxicity on human GIST cell lines and synergize with the TKI imatinib in vitro. Cilostazol also induces nuclear exclusion, hence inactivation, of the transcriptional co-activator YAP, in a cAMP-independent manner. Verteporfin, a YAP/TEAD interaction inhibitor, reduces by 90% the viability of both imatinib-sensitive GIST882 and imatinib-resistant GIST48 cells. Analysis of TMA indicated a nuclear localization, hence activation, of YAP in most GIST. These results highlight for the first time the role of YAP in GIST biology and the potential of compounds targeting PDE3A or YAP to tackle GIST resistance to tyrosine kinase inhibitors (TKI).

Nowadays, TKI resistance and escape under therapy remain major therapeutic challenges in GIST. Understanding the molecular and cellular mechanisms of cytotoxicity of repurposed drugs already in clinical use for other indications will provide the rational backbone for clinical studies to improve the targeted therapy for GIST patients in a near future.

Methods employed: Cell culture ; Viability assay ; Apoptosis & ferroptosis assay; Western blot; qPCR ; Sequencing; Tissue micro arrays; Immunohistochemistry; Immunofluorescence; Fluorescent protein; Mouse models; Light microscopy; Tissue clearing.