Gamma secretase dependent release of the CD44 cytoplasmic tail upregulates IFI16 in cd44-/- tumor cells, MEFs and macrophages

Abstract

The adhesion molecule and co-receptor of receptor tyrosine kinases, CD44, is expressed in all cells of the immune system, but also in numerous non-immune cells. CD44 plays roles in the cellular response to different pathogens. The molecular actions of CD44 during these processes are by and large still unknown. The CD44 molecule undergoes a sequential proteolytic cleavage which leads to the release of a soluble intracellular domain (CD44-ICD). Previous reports had shown that the CD44-ICD is taken up into the nucleus where it enhances transcription of specific target genes. By RNA profiling we identified a CD44-dependent transcriptional increase of interferon-responsive genes, among them IFI16. IFI16 is important in the innate immune response. It senses and binds pathogenic DNA and, together with cGAS, activates the cGAS-cGAMP-STING pathway and induces the expression of genes relevant for the response, e.g. IFN-β. Our results show that the enhancement of IFI16 expression depended on CD44 cleavage. A CD44-negative tumor cell line, embryonic fibroblasts and bone marrow-derived macrophages from cd44-/- mice were reduced in their response to IFN-γ, to viral DNA fragments and to Listeria monocytogenes infection. We could rescue the deficiency of CD44 negative RPM-MC cells and cd44-/- MEFs by expressing only the soluble CD44-ICD in the absence of any other CD44 domain. Expression of the CD44-ICD carrying a mutation that prevented the uptake into the nucleus, could not rescue the absence of CD44. This molecular aspect of regulation by CD44 may explain part of the immune phenotypes of mice with cd44 gene disruption.

Presenilins and γ-Secretase in Membrane Proteostasis

“…The best-understood example is the intracellular domain (ICD) of Notch that, when liberated from cellular membranes by γ-secretase cleavage, can translocate to the nucleus to regulate transcription and determine cell fate decisions [75,76]. Nuclear translocation, control of gene transcription, and modulation of intracellular signaling pathways have also been shown for the ICDs of the amyloid precursor protein (APP) [77,78], ErbB4 [79,80,81,82,83,84,85], CD44 [86,87,88,89,90,91,92], and ephrinB2 [93,94,95]. However, for most of the γ-secretase substrates, a physiological role for the cleavage products has not been identified, and it has been speculated that γ-secretase activity might also be important for the degradation of CTFs generated by ectodomain shedding that otherwise would remain in cellular membranes and potentially interfere with membrane dynamics [60,96].…”

Dysregulation of ADAM10 shedding activity in naked mole-rat fibroblasts is due to deficient phosphatidylserine externalisation

“…CD44 can be cleaved in the ectodomain by metalloproteases (Nagano et al, 2004; Nagano and Saya, 2004; Nakamura et al, 2004), resulting in a sequential proteolytic cleavage of the intracellular domain by γ-secretase, generating release of the CD44 intracellular domain fragment (CD44ICD) (Murakami et al, 2003), which translocates to the nucleus, regulating transcriptional activity through transcription factors as CBP/p300 and STAT3 (Okamoto et al, 2001). In addition, CD44ICD regulates the transcription of proteins like MMP-9 (Miletti-Gonzalez et al, 2012), IFN-γ (Schultz et al, 2018) and CD44 itself (Okamoto et al, 2001).…”

Proteolytic Processing of CD44 and Its Implications in Cancer

“…The correlation in mRNA and protein levels between CD44 and PD-L1 demonstrated that the binding of the ICD to the regulatory sequence of PD-L1 promotes its expression [ 82 ]. Since no transactivation domains have been found yet, it is believed that the ICD requires the participation of neighboring transcription factors [ 83 ].…”