Abstract
Epidermal differentiation is a complex process that requires the regulated and sequential expression of various genes. Most fused-type S100 proteins are expressed in the granular layer and it is hypothesized that these proteins may be associated with cornification and barrier formation. We previously identified a member of the fused-type S100 proteins, Trichohyalin-like 1 (TCHHL1) protein. TCHHL1 is distributed in the basal layer of the normal epidermis. Furthermore, the expression is markedly increased in cancerous/non-cancerous skin samples with the hyperproliferation of keratinocytes. We herein examined the role of TCHHL1 in normal human keratinocytes (NHKs) and squamous cell carcinoma (SCC). The knockdown of TCHHL1 by transfection with TCHHL1 siRNA significantly inhibited proliferation and induced the early apoptosis of NHKs. In TCHHL1-knockdown NHKs, the level of extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation was markedly decreased. In addition, the slight inhibition of v-akt murine thymoma viral oncogene homolog (AKT) phosphorylation and upregulation of forkhead box-containing protein O1(FOXO1), B-cell lymphoma2 (BCL2) and Bcl2-like protein 11 (BCL2L11) was observed. Skin-equivalent models built by TCHHL1-knockdown NHKs showed a markedly hypoplastic epidermis. These findings highlight that TCHHL1 plays an important role in homeostasis of the normal epidermis. TCHHL1 was expressed in the growing cells of cutaneous SCC; therefore, we next examined an association with the cell growth in HSC-1 cells (a human SCC line). In HSC-1 cells, the knockdown of TCHHL1 also suppressed cell proliferation and induced apoptosis. These cells showed an inhibition of phosphorylation of ERK1/2, AKT and signal transducers and activator of transcription 3, and the significant upregulation of FOXO1, BCL2, and BCL2L11. Accordingly, TCHHL1 is associated with survival of cutaneous SCC. In addition, we hypothesize that TCHHL1 may be a novel therapeutic target in cutaneous SCC.
Highlights
Epidermal differentiation is a complex process that requires the regulated and sequential expression of various genes
Trichohyalin-like 1 (TCHHL1) was previously reported to be expressed in the basal layer of the normal epidermis and the increased expression of TCHHL1 was observed in skin disorders with hyperproliferative keratinocytes[12]
These findings suggested an association between TCHHL1 and the proliferation of keratinocytes
Summary
Epidermal differentiation is a complex process that requires the regulated and sequential expression of various genes. The findings that mutation of the filaggrin gene causes ichthyosis vulgaris[9] or atopic dermatitis[10] and that the expression of filaggrin-like proteins is decreased in atopic skin[11] may support this hypothesis. TCHHL1 is expressed in the basal layer of the normal epidermis. The expression of TCHHL1 was increased in skin samples with the hyperproliferation of keratinocytes, such as psoriasis vulgaris, basal cell carcinoma, and squamous cell carcinoma (SCC)[12]. The expression of TCHHL1 was enhanced in the proliferating keratinocytes of the epidermis damaged by ultraviolet irradiation[13]. These findings suggest that TCHHL1 is associated with the proliferation of keratinocytes
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