Modulation of WI‐38 cell proliferation by elevated levels of CaCl₂

Abstract

Elevating the level of extracellular calcium (CaEx2+) increases the saturation density achieved by the normal human diploid cell line, WI-38, but does not change the growth rate. Day 7 cell yields remain unchanged when [CaEx2+] is between 0.5 mM and 3.0 mM, decrease when [CaEx2+] less than 0.5 mM, and increase when [CaEx2+] greater than 3.0 mM. Combining hydrocortisone with additional CaCl2 results in an additive effect on the saturation density relative to that obtained with each treatment separately. The stimulatory effect of elevated [CaCl2] is independent of serum concentration but is lost when WI-38 cells are grown in conditioned medium. Stimulation is recovered when conditioned medium is diluted with serum-free medium. In the case of young cultures grown in conditioned medium, stimulation can also be recovered when higher than usual levels of additional CaCl2 are used (2-3 mM). A glutamine supplementation to the conditioned medium potentiates cell response to elevated [CaCl2]. These results indicate that the loss of an enhanced saturation density when cells are grown in conditioned medium is not due to serum depletion but is more likely the effect of metabolites and/or nutrient depletion. When older or less vigorously growing cultures are grown in conditioned medium, additions of up to 3 mM CaCl2 only lead to inhibition, suggesting an age-related change in proliferative regulation. Elevated levels of CaEx2+ also enhance the proliferative response of quiescent monolayers to serum stimulation. This finding, along with the increase in saturation density of Ca2+-treated cultures, suggests that an elevated level of CaEx2+ affects cell entry into and exit from quiescence brought on by density-dependent inhibition.

All-trans retinoic acid (RA) stimulates events in organ-cultured human skin that underlie repair. Adult skin from sun-protected and sun-exposed sites responds in an identical manner to RA while neonatal foreskin responds differently.

“…Past studies have shown that proliferative responses of human keratinocytes and fibroblasts decrease as a function of age (1 -12 (13)(14)(15)(16). Changes in fibroblast and keratinocyte proliferative capacity in monolayer culture are correlated with age-related alterations in the appearance of the skin (17)(18)(19)(20)(21).…”

all-trans-Retinoic acid preserves viability of fibroblasts and keratinocytes in full-thickness human skin and fibroblasts in isolated dermis in organ culture

“…It seems reasonable to suggest that RA functions in some manner to overcome the limitation imposed by insufficient Ca 2+ on fibroblast function. While it is difficult to extrapolate from monolayer and organ culture data to what might occur in intact skin, one could postulate that a progressive decrease in responsiveness to extracellular Ca 2+ in dermal fibroblasts as a function of aging (noted in previous studies by others [4,5,[24][25][26]) provides a target of opportunity for retinoid action.…”

Stimulation of mono (ADP‐ribosyl)ation by reduced extracellular calcium levels in human fibroblasts

“…The growth of human diploid fibroblast-like cells (HDF) in culture can be modulated by a variety of culture conditions including the variation of the extracellular Ca2+ concentration. Elevated levels of extracellular Ca2+ increase the saturation density of HDF and enhance the proliferative response of quiescent monolayers to serum stimulation (Praeger and Cristofalo, 1986). Conversely, a reduction in extracellular Ca2+ arrests HDF in a quiescent Gl/GO cell-cycle state (Boynton et al, 1977;Tupper et al, 1980Tupper et al, , 1982.…”