Multiple outcomes of the germline p16INK4a mutation affecting senescence and immunity in human skin
Priya Subramanian1, Souraya Sayegh1, Phatthamon Laphanuwat1,2
1Division of Medicine, University College London, London, UK.
Abstract:
The integrated behaviour of multiple senescent cell types within a single human tissue leading to the development of malignancy is unclear. Patients with Familial Melanoma Syndrome (FMS) have heterozygous germline defects in the CDKN2A gene coding for the cyclin inhibitor p16INK4a. Melanocytes within skin biopsies from FMS patients express significantly less p16INK4a but express higher levels of the DNA-damage protein 𝛾H2AX a than fibroblastic cells. However, patient fibroblasts also exhibit defects since senescent cells do not increase in the skin during ageing and fibroblasts isolated from the skin of patients have increased replicative capacity compared to control fibroblasts in vitro, culminating in abnormal nuclear morphology. Patient derived fibroblasts also secreted less SASP than control cells. Predisposition of FMS patients to melanoma may therefore result from integrated dysregulation of senescence in multiple cell types in vivo. The inherently greater levels of DNA damage and the overdependence of melanocytes on p16 for cell cycle inhibition after DNA damage makes them exquisitely susceptible to malignant transformation. This may be accentuated by senescence-related defects in fibroblasts, in particular reduced SASP secretion that hinders recruitment of T cells in the steady state and thus reduces cutaneous immunosurveillance in vivo.
Insights
Familial Melanoma Syndrome involves defects in p16INK4a and senescence in skin cells. This integrated cellular dysfunction in melanocytes and fibroblasts may predispose FMS patients to melanoma development.
Area of Science:
- Oncology
- Genetics
- Cellular Biology
Background:
- Familial Melanoma Syndrome (FMS) is linked to germline defects in the CDKN2A gene, which encodes the p16INK4a protein.
- The role of integrated senescence in multiple cell types within human tissue in malignancy development is not fully understood.
Purpose of the Study:
- To investigate the integrated behavior of senescent melanocytes and fibroblasts in FMS patients.
- To understand how CDKN2A defects and cellular senescence contribute to melanoma predisposition.
Main Methods:
- Analysis of skin biopsies from FMS patients and controls.
- Assessment of p16INK4a and 𝛾H2AX levels in melanocytes and fibroblasts.
- In vitro studies on fibroblast replicative capacity and senescence-associated secretory phenotype (SASP).
Main Results:
- FMS melanocytes show reduced p16INK4a and increased DNA damage (𝛾H2AX).
- FMS fibroblasts exhibit increased replicative capacity, abnormal nuclear morphology, and reduced SASP secretion.
- Senescent cells do not increase in FMS patient skin during aging.
Conclusions:
- Integrated dysregulation of senescence in multiple cell types, particularly melanocytes and fibroblasts, may predispose FMS patients to melanoma.
- Melanocyte susceptibility to malignant transformation is heightened by reduced p16INK4a and increased DNA damage.
- Fibroblast defects, including reduced SASP, may impair cutaneous immunosurveillance, further contributing to melanoma risk.
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