Stromal cell-derived factor 1 expression in various skin tumours

A combined opposite targeting of p110δ PI3K and RhoA abrogates skin cancer

Malignant melanoma is the most aggressive and deadly skin cancer with an increasing incidence worldwide whereas SCC is the second most common non-melanoma human skin cancer with limited treatment options. Here we show that the development and metastasis of melanoma and SCC cancers can be blocked by a combined opposite targeting of RhoA and p110δ PI3K. We found that a targeted induction of RhoA activity into tumours by deletion of p190RhoGAP-a potent inhibitor of RhoA GTPase-in tumour cells together with adoptive macrophages transfer from δD910A/D910A mice in mice bearing tumours with active RhoA abrogated growth progression of melanoma and SCC tumours. Τhe efficacy of this combined treatment is the same in tumours lacking activating mutations in BRAF and in tumours harbouring the most frequent BRAF(V600E) mutation. Furthermore, the efficiency of this combined treatment is associated with decreased ATX expression in tumour cells and tumour stroma bypassing a positive feedback expression of ATX induced by direct ATX pharmacological inactivation. Together, our findings highlight the importance of targeting cancer cells and macrophages for skin cancer therapy, emerge a reverse link between ATX and RhoA and illustrate the benefit of p110δ PI3K inhibition as a combinatorial regimen for the treatment of skin cancers.

PDGFR-induced autocrine SDF-1 signaling in cancer cells promotes metastasis in advanced skin carcinoma

Advanced and undifferentiated skin squamous cell carcinomas (SCCs) exhibit aggressive growth and enhanced metastasis capability, which is associated in mice with an expansion of the cancer stem-like cell (CSC) population and with changes in the regulatory mechanisms that control the proliferation and invasion of these cells. Indeed, autocrine activation of PDGFRα induces CSC invasion and promotes distant metastasis in advanced SCCs. However, the mechanisms involved in this process were unclear. Here, we show that CSCs of mouse advanced SCCs (L-CSCs) express CXCR4 and CXCR7, both receptors of SDF-1. PDGFRα signaling induces SDF-1 expression and secretion, and the autocrine activation of this pathway in L-CSCs. Autocrine SDF-1/CXCR4 signaling induces L-CSC proliferation and survival, and mediates PDGFRα-induced invasion, promoting in vivo lung metastasis. Validation of these findings in patient samples of skin SCCs shows a strong correlation between the expression of SDF1, PDGFRA, and PDGFRB, which is upregulated, along CXCR4 in tumor cells of advanced SCCs. Furthermore, PDGFR regulates SDF-1 expression and inhibition of SDF-1/CXCR4 and PDGFR pathways blocks distant metastasis of human PD/S-SCCs. Our results indicate that functional crosstalk between PDGFR/SDF-1 signaling regulates tumor cell invasion and metastasis in human and mouse advanced SCCs, and suggest that CXCR4 and/or PDGFR inhibitors could be used to block metastasis of these aggressive tumors.

Dermal fibroblast expression of stromal cell-derived factor-1 (SDF-1) promotes epidermal keratinocyte proliferation in normal and diseased skin

Stromal cells provide a crucial microenvironment for overlying epithelium. Here we investigated the expression and function of a stromal cell-specific protein, stromal cell-derived factor-1 (SDF-1), in normal human skin and in the tissues of diseased skin. Immunohistology and laser capture microdissection (LCM)-coupled quantitative real-time RT-PCR revealed that SDF-1 is constitutively and predominantly expressed in dermal stromal cells in normal human skin in vivo. To our surprise, an extremely high level of SDF-1 transcription was observed in the dermis of normal human skin in vivo, evidenced by much higher mRNA expression level than type I collagen, the most abundant and highly expressed protein in human skin. SDF-1 was also upregulated in the tissues of many human skin disorders including psoriasis, basal cell carcinoma (BCC), and squamous cell carcinoma (SCC). Double immunostaining for SDF-1 and HSP47 (heat shock protein 47), a marker of fibroblasts, revealed that fibroblasts were the major source of stroma-cell-derived SDF-1 in both normal and diseased skin. Functionally, SDF-1 activates the ERK (extracellular-signal-regulated kinases) pathway and functions as a mitogen to stimulate epidermal keratinocyte proliferation. Both overexpression of SDF-1 in dermal fibroblasts and treatment with rhSDF-1 to the skin equivalent cultures significantly increased the number of keratinocyte layers and epidermal thickness. Conversely, the stimulative function of SDF-1 on keratinocyte proliferation was nearly completely eliminated by interfering with CXCR4, a specific receptor of SDF-1, or by knock-down of SDF-1 in fibroblasts. Our data reveal that extremely high levels of SDF-1 provide a crucial microenvironment for epidermal keratinocyte proliferation in both physiologic and pathologic skin conditions.

The human cutaneous chemokine system

Irrespective of the immune status, the vast majority of all lymphocytes reside in peripheral tissues whereas those present in blood only amount to a small fraction of the total. It has been estimated that T cells in healthy human skin outnumber those present in blood by at least a factor of two. How lymphocytes within these two compartments relate to each other is not well understood. However, mounting evidence suggest that the study of T cell subsets present in peripheral blood does not reflect the function of their counterparts at peripheral sites. This is especially true under steady-state conditions whereby long-lived memory T cells in healthy tissues, notably those in epithelial tissues at body surfaces, are thought to fulfill a critical immune surveillance function by contributing to the first line of defense against a series of local threats, including microbes, tumors, and toxins, and by participating in wound healing. The relative scarcity of information regarding peripheral T cells and the factors regulating their localization is primarily due to inherent difficulties in obtaining healthy tissue for the extraction and study of immune cells on a routine basis. This is most certainly true for humans. Here, we review our current understanding of T cell homing to human skin and compare it when possible with gut-selective homing. We also discuss candidate chemokines that may account for the tissue selectivity in this process and present a model whereby CCR8, and its ligand CCL1, selectively regulate the homeostatic migration of memory lymphocytes to skin tissue.