Unraveling the interplay between senescent dermal fibroblasts and cutaneous squamous cell carcinoma cell lines at different stages of tumorigenesis

Cutaneous Squamous Cell Carcinoma (cSCC) is the second most common type of non-melanoma skin cancer in white-skinned populations. cSCC is associated with sun exposure and aging, which is concomitant with an accumulation of senescent cells in the skin. The involvement of senescent cells in carcinogenesis has been highlighted in several cancer types and an interaction between cSCC cells and senescent cells is proposed, but still little explored. Tumor-associated effects are mostly attributed to the senescence-associated secretory phenotype (SASP). Here, we compared two in vitro models of senescence, namely replicative senescence and UVB-stress induced premature senescence (UVB-SIPS), in human dermal fibroblasts and screened for expression of SASP-related genes in our models. Next, the impact of senescent fibroblasts on three cSCC isogenic cell lines, representing different stages of keratinocyte malignant transformation, was studied. Only a limited impact on cSCC cell lines' growth and migration has been detected with conditioned media collected from senescent fibroblasts and indirect co-cultures. We then investigated the opposite interaction and found that cSCC cell lines maintained in indirect co-cultures with fibroblasts induced and reinforced their senescence state as shown by an increased proportion of cells positive for the senescence-associated β-galactosidase activity and an increased expression of several SASP-related genes. Moreover, these effects were modulated according to the stage of tumorigenesis of the different cSCC cell lines used. Finally, cSCC cell lines-co-cultures are associated with NF-κB activation in HDFs. Understanding the interplay between tumor cells and their microenvironment may have important influences in cancer research and therapeutic strategies.