Selective migration of terminally differentiating cells from the basal layer of cultured human epidermis.

Abstract

How terminally differentiating cells are selectively expelled from the basal layer of epidermis has been a source of interest and speculation for many years . The problem can now be studied in culture, using involucrin synthesis as an early marker of terminal differentiation in human keratinocytes . When keratinocytes are forced to grow as a monolayer by reducing the calcium ion concentration of the culture medium, they still begin to synthesize involucrin . Raising the level of calcium ions induces stratification, and cells that are synthesizing involucrin are selectively expelled from the basal layer. I have found that during calciuminduced stratification no new proteins or glycoproteins are synthesized, and the rate of cell division does not change . Movement of involucrin-positive cells out of the basal layer was found to be unaffected by cycloheximide, tunicamycin, or cytosine arabinoside . These results suggest that keratinocytes growing as a monolayer already have the necessary properties to determine their position when stratification is induced . Addition of calcium simply allows formation of desmosomes and other intimate cell contacts required for stratification . The properties of involucrin-positive cells that determine their suprabasal position include a reduced affinity for the culture substrate and preferential adhesion to other cells at the same stage of terminal differentiation . The molecular basis of these adhesive changes is discussed .

Epidermal differentiation: the bare essentials.

“…While this notion seems plausible, this simple model does not account for why there are two to three layers of cells with biochemical and morphological characteristics of basal cells in squamous cell carcinoma cells cultured on floating lattices of collagen and fibroblasts (Stoler et al, 1988;Kopan and Fuchs, 1989). Moreover, it does not explain why certain features of epidermal differentiation can be induced in basal cells before their exit from the innermost layer (Watt, 1984;Roop et al, 1987;Choi and Fuchs, 1990). Thus, it seems more likely that cessation of cell division can be uncoupled from loss of basement membrane contact and is key to when a cell shifts to a program of gene expression leading to terminal differentiation.…”

“…Thus for example, when human cells are cultured in low calcium medium, withdrawal from the cell cycle and involucrin synthesis still occur (Watt, 1984). Similarly, while desmosomes cannot assemble in low calcium, desmosomal proteins are nevertheless synthesized in both low and high calcium medium Duden and Franke, 1988).…”

Upregulation of CD26 expression in epithelial cells and stromal cells during wound-induced skin tumour formation

“…CD26 is expressed in the differentiating epidermal layers and thus the upregulation in InvEE transgenic mice is correlated with the increased number of differentiated cell layers. The observation that raising the level of calcium ions in the culture medium leads to increased CD26 activity in cultured keratinocytes supports this conclusion, as calcium is known to stimulate intercellular adhesion and promote epidermal stratification (Watt, 1984). Elevated levels of CD26 protein correlated with elevated CD26 activity in InvEE epidermal lysates, even though CD26 was differently glycosylated in WT and InvEE epidermis.…”

“…To test this, we increased the level of calcium ions in the culture medium, which induces stratification and assembly of intercellular adhesive junctions (Watt, 1984). As shown in Figure 2d, increasing the level of calcium ions increased CD26 activity in both InvEE and WT keratinocytes.…”

Characterization of the calcium sensitivity of differentiation in SCC-13 human squamous carcinoma cells

“…lack of stratification and absence of desmosomes (6), are evident in normal human epidermal cells under similar conditions (2,15). In the human cells calcium regulates the organization of intracellular structural components such as desmosomes and keratins (26,28). However, at least some cellular maturation occurs in low-calcium medium because a substantial fraction of the cells enlarge and produce the human envelope precursor, involucrin (27).…”