The human Flower isoform hFWE4 facilitates cornification in cutaneous squamous cell carcinoma
Cutaneous squamous cell carcinoma (cSCC) is the second most common human tumor and arises from keratinocytes that comprise the epidermis and its associated hair follicles. Remarkably, transformed keratinocytes within a cSCC retain some ability to execute the terminal differentiation program that typically generates a stratified epidermis. Instead of the polarized stratification towards the body surface seen in normal epidermis, cSCC keratinocytes differentiate concentrically inward to produce keratin pearls. It is well appreciated that cSCC differentiation status is correlated with degree of local invasion and potential for distant metastasis, with well differentiated tumors having a better prognosis. While molecular mechanisms that govern the differentiation process are incompletely understood, identifying candidate molecules associated with cSCC differentiation can provide new histologic markers for prognostic stratification. Here we demonstrate that Flower (FWE), a newly described regulator of lamellar body (LB) trafficking in normal epidermis, is specifically expressed within highly differentiated layers of cSCC. Genetic knockout of the hFWE gene dysregulates cornification and LB-related gene expression leading to abnormal keratinization patterns, while ectopic hFWE4 expression drives G1-arrest and exit from the proliferative basal keratinocyte population. Additionally, we find that poorly differentiated keratinocyte regions of human cSCC exhibit minimal FWE-positivity, while this population is readily detectable in well-differentiated regions. We propose that FWE represents a novel differentiation marker in cSCC that could be utilized for classifying differentiation status and prognostic stratifying these tumors.