Interplay between Podoplanin, CD44s and CD44v in Squamous Carcinoma Cells

Abstract

Podoplanin and CD44 are transmembrane glycoproteins involved in inflammation and cancer. In this paper, we report that podoplanin is coordinately expressed with the CD44 standard (CD44s) and variant (CD44v) isoforms in vivo—in hyperplastic skin after a pro-inflammatory stimulus with 12-O-tetradecanoylphorbol-13-acetate (TPA)—and in vitro—in cell lines representative of different stages of mouse-skin chemical carcinogenesis, as well as in human squamous carcinoma cell (SCC) lines. Moreover, we identify CD44v10 in the mouse-skin carcinogenesis model as the only CD44 variant isoform expressed in highly aggressive spindle carcinoma cell lines together with CD44s and podoplanin. We also characterized CD44v3-10, CD44v6-10 and CD44v8-10 as the major variant isoforms co-expressed with CD44s and podoplanin in human SCC cell lines. Immunofluorescence confocal microscopy experiments show that these CD44v isoforms colocalize with podoplanin at plasma membrane protrusions and cell–cell contacts of SCC cells, as previously reported for CD44s. Furthermore, CD44v isoforms colocalize with podoplanin in chemically induced mouse-skin SCCs in vivo. Co-immunoprecipitation experiments indicate that podoplanin physically binds to CD44v3-10, CD44v6-10 and CD44v8-10 isoforms, as well as to CD44s. Podoplanin–CD44 interaction is mediated by the transmembrane and cytosolic regions and is negatively modulated by glycosylation of the extracellular domain. These results point to a functional interplay of podoplanin with both CD44v and CD44s isoforms in SCCs and give insight into the regulation of the podoplanin–CD44 association.

Fibroblastic Reticular Cell Response to Dendritic Cells Requires Coordinated Activity of Podoplanin, CD44 and CD9

“…Since podoplanin is induced to cluster in cholesterol-rich regions upon CLEC-2 binding (2), we hypothesised that membrane partner proteins of podoplanin may also be required to downregulate podoplanin-driven contractility for FRC network elongation. A known partner protein of podoplanin, the hyaluronic acid receptor CD44 (19, 20), is also specifically upregulated on TRCs, but not on MRCs or LECs (Fig. 1e-g).…”

“…It is reported that podoplanin and CD44 can directly interact via either their extracellular domains (19), or their transmembrane and cytoplasmic domains (20). Podoplanin and CD9 are also confirmed as direct partner proteins, interacting through the transmembrane domain of podoplanin and CD9 transmembrane domains 1 and 2 (21).…”

“…Here, we found that two known podoplanin partner proteins, the hyaluronan receptor CD44 (19, 20) and tetraspanin CD9 (21), are transcriptionally regulated in response to CLEC-2, and their expression is controlled on the surface of FRC populations in vivo during an immune response. In other biological contexts, CD44 and CD9 link extracellular cues to intracellular signalling.…”

“…To date, no function of CD9 has been assigned to FRC biology. The interaction of podoplanin with CD44 is mediated by their extracellular domains (19), but it was recently reported to also involve transmembrane and cytosolic regions (20). The podoplanin/CD44 interaction at tumour cell protrusions promotes cancer cell migration (19).…”

Abnormal Glycosylation of Cancer Stem Cells and Targeting Strategies

“…For example, a Phase I clinical trial with Maackia amurensis seed lectin (MASL), which can target podoplanin, is set to start for the treatment of squamous cell carcinoma of head and neck (NCT04188665) (163,164). Podoplanin is a mucin like sialoglycoprotein, co-expressed with CSC marker CD44 and CD44v (165). However, lectins may also bind to healthy cells presenting SA.…”