Cell cultures in uterine leiomyomas: Rapid disappearance of cells carrying MED12 mutations

Abstract

Uterine leiomyomas (UL) are the most frequent symptomatic human tumors. Nevertheless, their molecular pathogenesis is not yet fully understood. To learn more about the biology of these common neoplasms and their response to treatment, cell cultures derived from UL are a frequently used model system, but until recently appropriate genetic markers confirming their origin from the tumor cell population were lacking for most UL, i.e., those not displaying karyotypic abnormalities. The identification of MED12 mutations in the majority of UL makes it possible to trace the tumor cell population during in vitro passaging in the absence of cytogenetic abnormalities. The present study is addressing the in vitro survival of cells carrying MED12 mutations and its association with karyotypic alterations. The results challenge numerous in vitro studies into the biology and behavior of leiomyomas. Cells of one genetic subtype of UL, i.e., those with rearrangements of the high mobility AT-hook 2 protein gene (HMGA2), seem to be able to proliferate in vitro for many passages whereas tumor cells from the much more frequent MED12-mutated lesions barely survive even the first passages. Apparently, for the most frequent type of human UL no good in vitro model seems to exist because cells do not survive culturing. On the other hand, this inability may point to an Achilles' heel of this type of UL.

Factors affecting the loss of MED12-mutated leiomyoma cells during in vitro growth

“…While UL-derived cell cultures are a wide-spread model system for research into the pathogenesis and behavior of the tumors [2, 9–11] recent results challenge the usefulness of this model for the group of tumors carrying MED12 mutations. Contrary to the expectations a rapid loss of mutated cells accompanied in vitro growth of UL-derived cell cultures [12]. As a rule, the mutations were not even detectable after early passages of in vitro growth resulting from so far unknown mechanisms.…”

“…This latter type of mutation occasionally can co-exist with chromosomal alterations except for those targeting HMGA2 [3–7] and clearly represents the most common type of driver mutations in UL. In vitro cells with this type of driver mutation recently were shown to coincide with a strictly reduced growth capacity in vitro , leading to their rapid disappearance in cell culture [12, 20]. In contrast, other cells from the samples not carrying these mutations of presumed non-tumorigenic origin as well as from tumors carrying HMGA2 rearrangements can survive much longer [12, 20].…”

Subtype-Specific Tumor-Associated Fibroblasts Contribute to the Pathogenesis of Uterine Leiomyoma

“…The high concentration of TAFs explains why MED12 mutant cells are quickly lost from the primary culture of LMs (25,26); fibroblasts attach the culture dish better and grow faster than SMCs in standard culture conditions, conditions originally developed to optimize fibroblast growth (27). Overgrowth of fibroblasts is a classic problem for the primary culturing of SMCs including MM, and many techniques to repress the growth of fibroblasts in SMC culture have been proposed (20,28–32).…”

“…The study by Bloch et al also suggested that the loss of MED12 mutant cells is partially due to the detachment of mutant cells from the culture flask, which likely reflects the weaker adherence of SMCs to the plastic surface compared to fibroblasts (40). Then, the subsequent passaging further dilutes SMCs in MED12-LM cell culture (25). Conversely, the low fibroblast concentration in HMGA2-LMs explains why HMGA2 mutant cells can be maintained in vitro for multiple passages (25).…”

“…Then, the subsequent passaging further dilutes SMCs in MED12-LM cell culture (25). Conversely, the low fibroblast concentration in HMGA2-LMs explains why HMGA2 mutant cells can be maintained in vitro for multiple passages (25). …”