Targeting Perlecan in Human Keratinocytes Reveals Novel Roles for Perlecan in Epidermal Formation

Abstract

Heparin-binding growth factors are crucial for the formation of human epidermis, but little is known about the role of heparan sulfate proteoglycans in this process. Here we investigated the role of the heparan sulfate proteoglycan, perlecan, in the formation of human epidermis, by utilizing in vitro engineered human skin. By disrupting perlecan expression either in the dermis or the epidermis, we found that epidermally derived perlecan is essential for epidermal formation. Perlecan-deficient keratinocytes formed a strikingly thin and poorly organized epidermis because of premature apoptosis and failure to complete their stratification program. Exogenous perlecan fully restored epidermal formation. Perlecan deposition in the basement membrane zone correlated with formation of multilayered epidermis. Perlecan deficiency, however, had no effect on the lining and deposition of major basement membrane components as was evident by a continuous linear staining of laminin and collagen IV. Similarly, perlecan deficiency did not affect the distribution of ␤1 integrin. Addition of the perlecan ligand, fibroblast growth factor 7, protected perlecan-deficient keratinocytes from cell death and improved the thickness of the epidermis. Taken together, our results revealed novel roles for perlecan in epidermal formation. Perlecan regulates both the survival and terminal differentiation steps of keratinocytes. Our results suggested a model whereby perlecan regulates these processes via controlling the bioavailability of perlecan-binding soluble factors involved in epidermal morphogenesis.Skin is the largest organ of the body. It serves as a shield against microorganism invasion and UV radiation, prevents dehydration, regulates body temperature, and is a part of the immune system (1). It consists of two distinct tissues, epidermis and dermis that are separated by a basement membrane (BM). 4 The dermis is a dense collagen-rich connective tissue that provides the support and nourishment to the overlying epidermis. It is mainly composed of fibroblasts that synthesize and secrete the various extracellular matrix (ECM) components (2). The epidermis is made primarily of keratinocytes that form a stratified squamous epithelium. It consists of multiple layers exhibiting distinct morphology and function. From the innermost to the outermost layers, they are the basal, spinous, granular, and cornified strata (3). Throughout adult life, the epidermis undergoes continuous self-renewal through proliferation of the basal cells, the only cells of the epidermis with the ability to proliferate. The keratinocytes undergo terminal differentiation as they leave the basal layer and move upward through the suprabasal layers toward the tissue surface, where they die and are sloughed off (3). This process makes the skin an excellent model system to study the coordinated regulation of cell proliferation, cell differentiation, and cell death. The formation of the mature epidermis is regulated by cross-talk with the adjacent connective tissue through a netw...

Targeting a Tumor-Specific Laminin Domain Critical for Human Carcinogenesis

“…It is possible that G45 promotes laminin-332 deposition in SCC directly by anchoring the laminin-332 molecule to the matrix during the process of BMZ assembly. Laminin-332 G45 domain (41) has heparin-binding properties (42) and may have the ability to bind with extracellular heparan sulfate proteoglycan BMZ components, such as perlecan (43) or dystroglycan (44). However, even in the absence of G45, laminin-332 deposition was shown to be restored to near WT levels in SCC tumors through activation of the PI3K pathway.…”

Downregulation of Sef, an inhibitor of receptor tyrosine kinase signaling, is common to a variety of human carcinomas

“…(B and C) hSef expression pattern. Probe preparation and RNA in-situ hybridization conditions have previously been described (Sher et al, 2006). The hybridization probe spanned nucleotides 1606-2208 of the hSef common coding region (accession # AY489047).…”

Importance of Extracellular Matrix Protein 1 (ECM1) in Maintaining the Functional Integrity of the Human Skin

“…The expression of ECM1a was found in the epidermal basal layer, in dermal blood vessels, the outer root sheath of hair follicles and in sebaceous lobules and epithelium of sweat glands, while ECM1b was expressed in the suprabasal layers of the epidermis. ECM1 is also capable of binding with perlecan, an important intrinsic molecule in skin organogenesis [8,44]. These observations suggest a crucial role for ECM1 in epidermal differentiation [5,7].…”

“…It is known that heparin-binding growth factors like perlecan are involved in organogenesis [44]. In vitro and in vivo experiments have shown that ECM1 is not essential for normal epidermal differentiation [45].…”