ERRα induces H3K9 demethylation by LSD1 to promote cell invasion.

Lysine Specific Demethylase 1 (LSD1) removes mono- and dimethyl groups from lysine 4 of histone H3 (H3K4) or H3K9, resulting in repressive or activating (respectively) transcriptional histone marks. The mechanisms that control the balance between these two antagonist activities are not understood. We here show that LSD1 and the orphan nuclear receptor estrogen-related receptor α (ERRα) display commonly activated genes. Transcriptional activation by LSD1 and ERRα involves H3K9 demethylation at the transcriptional start site (TSS). Strikingly, ERRα is sufficient to induce LSD1 to demethylate H3K9 in vitro. The relevance of this mechanism is highlighted by functional data. LSD1 and ERRα coregulate several target genes involved in cell migration, including the MMP1 matrix metallo-protease, also activated through H3K9 demethylation at the TSS. Depletion of LSD1 or ERRα reduces the cellular capacity to invade the extracellular matrix, a phenomenon that is rescued by MMP1 reexpression. Altogether our results identify a regulatory network involving a direct switch in the biochemical activities of a histone demethylase, leading to increased cell invasion.

Estrogen-related receptor α decreases RHOA stability to induce orientated cell migration.

Several physiopathological processes require orientated cellular migration. This phenomenon highly depends on members of the RHO family of GTPases. Both excessive and deficient RHO activity impair directional migration. A tight control is thus exerted on these proteins through the regulation of their activation and of their stability. Here we show that the estrogen-related receptor α (ERRα) directly activates the expression of TNFAIP1, the product of which [BTB/POZ domain-containing adapter for Cullin3-mediated RhoA degradation 2 (BACURD2)] regulates RHOA protein turnover. Inactivation of the receptor leads to enhanced RHOA stability and activation. This results in cell disorientation, increased actin network, and inability to form a lamellipodium at the migration edge. As a consequence, directional migration, but not cell motility per se, is impaired in the absence of the receptor, under pathological as well as physiological conditions. Altogether, our results show that the control exerted by ERRα on RHOA stability is required for directional migration.

The atypical alpha2beta2 IGF receptor expressed in inducible c2.7 myoblasts is derived from post-translational modifications of the mouse IGF-I receptor.

OBJECTIVE: Unlike parental permissive C2.7 myoblasts, inducible C2.7 myoblasts require IGF-I or IGF-II to differentiate and expression of MyoD is not constitutive. Our previous studies indicated that inducible myoblasts express an atypical alpha2beta2 IGF receptor that differs from the classical IGF-I receptor by its higher affinity for IGF-II compared with IGF-I and the higher molecular weight of its alpha and beta subunits. Expression of this atypical IGF-I receptor is developmentally regulated; hence this receptor is lost upon terminal differentiation. Muscle cell differentiation is a system in which IGF-II plays an essential role and developmentally regulated atypical IGF-I receptor may represent a candidate for mediating differentiation signals provided by IGF-II. To further understand the structure and the role of the atypical IGF-I receptor, (i) we investigated for a putative IGF-I receptor transcript polymorphism by extensive sequencing of RT-PCR products; (ii) we overexpressed cloned mouse IGF-I receptor in permissive and inducible C2.7 myoblasts and characterized the binding and structural properties of overexpressed IGF-I receptor and (iii) we analysed the effects of this overexpression on myoblasts differentiation. DESIGN: Cultured mouse myoblasts C2.7 and subclone variant inducible C2.7 cell lines were used. Mouse IGF-I receptor cDNA was cloned by cDNA library screening. Gene expression was measured by semi-quantitative RT-PCR analysis and receptor affinity by ligand binding. Receptor protein autophosphorylation of IGF-IR was analysed by immunoprecipitation and Western blot. Myoblastic differentiation was accessed by myogenic factors expression and immunofluorescence study. RESULTS: Atypical IGF-I receptor may correspond to a new receptor belonging to the insulin/IGF-I receptor family, or it may also derive from alternate splicing of the gene of the insulin/IGF-I receptors and/or post-translational modifications of the insulin/IGF-I receptors. Our results exclude the existence of a polymorphism of the IGF-I receptor transcripts in inducible and permissive myoblasts. In embryo and cancer cells IGF-II binds to insulin receptor (IR) isoform A, RT-PCR experiments show that IR is expressed in permissive but not in inducible myoblasts. We demonstrated here that post-translational processing of the mouse IGF-I receptor is responsible for the existence of the mouse atypical IGF-I receptor in inducible myoblasts. Overexpressed mouse IGF-I receptor in permissive myoblasts has the same biochemical and binding characteristics as the classical IGF-I receptor whereas in inducible myoblasts, overexpressed mouse IGF-I receptor has the biochemical, binding and functional characteristics of the atypical IGF-I receptor. CONCLUSIONS: Our results provide experimental evidence that the atypical IGF-I receptor variant expressed in subclone inducible C2.7 is issued from a post-translational processing of mouse IGF-I receptor. We show that this post-translational modification is closely associated with the cell lines indeed permissive C2.7 myoblasts process mouse cDNA IGF-I receptor as a classical IGF-I receptor whereas inducible C2.7 myoblasts process mouse cDNA IGF-I receptor as an atypical IGF-I receptor. On other hand, we show that overexpression of mouse IGF-I receptor in inducible myoblasts does not abrogate IGF-I or IGF-II requirement to differentiate.

miR-135a Inhibits the Invasion of Cancer Cells via Suppression of ERRα.

MicroRNA-135a (miR-135a) down-modulates parameters of cancer progression and its expression is decreased in metastatic breast cancers (as compared to non-metastatic tumors) as well as in prostate tumors relative to normal tissue. These expression and activity patterns are opposite to those of the Estrogen-Related Receptor α (ERRα), an orphan member of the nuclear receptor family. Indeed high expression of ERRα correlates with poor prognosis in breast and prostate cancers, and the receptor promotes various traits of cancer aggressiveness including cell invasion. Here we show that miR-135a down-regulates the expression of ERRα through specific sequences of its 3'UTR. As a consequence miR-135a also reduces the expression of downstream targets of ERRα. miR-135a also decreases cell invasive potential in an ERRα-dependent manner. Our results suggest that the decreased expression of miR-135a in metastatic tumors leads to elevated ERRα expression, resulting in increased cell invasion capacities.

Repression of osteoblast maturation by ERRα accounts for bone loss induced by estrogen deficiency.

ERRα is an orphan member of the nuclear receptor family, the complete inactivation of which confers resistance to bone loss induced by ageing and estrogen withdrawal to female mice in correlation with increased bone formation in vivo. Furthermore ERRα negatively regulates the commitment of mesenchymal cells to the osteoblast lineage ex vivo as well as later steps of osteoblast maturation. We searched to determine whether the activities of ERRα on osteoblast maturation are responsible for one or both types of in vivo induced bone loss. To this end we have generated conditional knock out mice in which the receptor is normally present during early osteoblast differentiation but inactivated upon osteoblast maturation. Bone ageing in these animals was similar to that observed for control animals. In contrast conditional ERRαKO mice were completely resistant to bone loss induced by ovariectomy. We conclude that the late (maturation), but not early (commitment), negative effects of ERRα on the osteoblast lineage contribute to the reduced bone mineral density observed upon estrogen deficiency.