Mediator Kinase Disruption in MED12-Mutant Uterine Fibroids From Hispanic Women of South Texas

CONTEXT

Mutations in the gene encoding Mediator complex subunit MED12 are dominant drivers of uterine fibroids (UFs) in women of diverse racial and ethnic origins. Previously, we showed that UF-linked mutations in MED12 disrupt its ability to activate cyclin C-CDK8/19 in Mediator. However, validation of Mediator kinase disruption in the clinically relevant setting of MED12-mutant UFs is currently lacking.

OBJECTIVE

The objective of this study was twofold. First, to extend the ethnic distribution profile of MED12 mutations by establishing their frequency in UFs from Hispanic women of South Texas. Second, to examine the impact of MED12 mutations on Mediator kinase activity in patient-derived UFs.

METHODS

We screened 219 UFs from 76 women, including 170 tumors from 57 Hispanic patients, for MED12 exon 2 mutations, and further examined CDK8/19 activity in Mediator complexes immunoprecipitated from MED12 mutation-negative and MED12 mutation-positive UFs.

RESULTS

MED12 exon 2 mutations in UFs from Hispanic women are somatic in nature, predominantly monoallelic, and occur at high frequency (54.1%). We identified a minimal cyclin C-CDK8 activation domain on MED12 spanning amino acids 15 through 80 that includes all recorded UF-linked mutations in MED12, suggesting that disruption of Mediator kinase activity is a principal biochemical defect arising from these pathogenic alterations. Analysis of Mediator complexes recovered from patient UFs confirmed this, revealing that Mediator kinase activity is selectively impaired in MED12-mutant UFs.

CONCLUSIONS

MED12 mutations are important drivers of UF formation in Hispanic women of South Texas. MED12 mutations disrupt Mediator kinase activity, implicating altered CDK8/19 function in UF pathogenesis.

Purification of mediator from HeLa cell lines expressing a flag-tagged mediator subunit

The Mediator (Med) complex plays a key role in promoter-specific activation of transcription by RNA polymerase II (Pol II). Med is a major target of activators and can be used in many types of affinity binding and immobilized template studies to evaluate interactions with individual activators. Additionally, all of the Med subunits have been cloned and can be subjected to individual structure-function analyses to learn how a specific activator interacts with a particular subunit. This protocol presents a simple affinity-based method to purify Med complex from HeLa cells stably expressing the Flag-tagged Intersex protein.