c-Met recruits ICAM-1 as a coreceptor to compensate for the loss of CD44 in Cd44 null mice

Area of Science:

• Cell biology
• Molecular biology
• Biochemistry

Background:

• CD44 isoforms function as coreceptors for receptor tyrosine kinases like c-Met and VEGFR-2.
• Cd44 knockout mice lack overt phenotypes, suggesting compensatory mechanisms.
• The role of CD44 in c-Met signaling and potential compensation pathways remain unclear.

Purpose of the Study:

• To identify factors compensating for CD44's role as a c-Met coreceptor in CD44-null mice.
• To investigate the functional substitution of CD44 by other molecules in c-Met signaling.

Main Methods:

• RNA interference (RNAi) technology
• Blocking experiments using antibodies, peptides, and purified ectodomains
• Overexpression studies
• Analysis of liver cell proliferation and c-Met activation in wild-type and Cd44 knockout mice after partial hepatectomy.

Main Results:

• Intercellular adhesion molecule-1 (ICAM-1) identified as a novel c-Met coreceptor in CD44-negative cells and hepatocytes from Cd44 null mice.
• CD44v6-specific antibodies inhibited liver cell proliferation and c-Met activation in wild-type mice.
• ICAM-1-specific antibodies inhibited liver cell proliferation and c-Met activation in Cd44 knockout mice.
• Demonstrated functional substitution of CD44v6 by ICAM-1 in Cd44 null mice.

Conclusions:

• ICAM-1 compensates for CD44v6 as a coreceptor for c-Met in Cd44 null mice.
• This study provides experimental evidence for functional substitution of a protein by a heterologous one in a knockout mouse model.
• Highlights the importance of compensatory mechanisms in explaining the absence of phenotypes in knockout studies.