We describe a new Swiss 3T3 preadipose clone, 3T3-F442A/C4, which shows higher sensitivity to serum adipogenic factors and to human growth hormone as compared to other 3T3 preadipose clones. The 3T3-F442A/C4 clone exhibited several characteristics different from the parental 3T3-F442A cells, mainly a high extent of adipose conversion under culture conditions that are non-adipogenic for the parental cells. The 3T3-F442A/C4 cells are not committed to undergo adipose differentiation, since they do not differentiate into adipocytes under serum-free or low-serum culture conditions, unless adipogenic factors or growth hormone are added into the culture medium. The 3T3-F442A/C4 cells showed 1.5- to 3.6-fold higher sensitivity to serum adipogenic factors and 5- to 6-fold higher sensitivity to human growth hormone as compared to the 3T3-F442A cells. The 3T3-F442A/C4 variant clone also differed from the parental clone by having a shorter population doubling time, an increased saturation density, and lower activity levels in some biochemical markers of adipose differentiation. On the other hand, the new variant clone has a similar proportion of cells susceptible to become adipocytes, and a similar response to insulin as compared to the parental cells. Our results show that the 3T3-F442A/C4 cells represent a new 3T3 preadipose clone that could be useful as a bioassay to evaluate growth hormone activity, as well as to purify and characterize hormones, adipogenic factors, and those compounds that affect mammalian adipogenesis.

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