E2F1 and TFDP1 Regulate PITX1 Expression in Normal and Osteoarthritic Articular Chondrocytes

Abstract

We previously reported a loss-of-PITX1 expression in patients suffering of knee/hip osteoarthritis (OA). Search for the mechanism underlying this event led us to discover that PITX1 repression was triggered by the aberrant nuclear accumulation of Prohibitin (PHB1), an E2F1 co-repressor, in OA articular chondrocytes. In the current study, we assessed in details the involvement of E2F transcription factors in regulating PITX1 expression. We also analyzed other genes that are similarly regulated by E2F in regard to osteoarthritis. The transcriptional regulation of the PITX1 promoter by E2F1 was analyzed with the luciferase reporter assay, and chromatin immunoprecipitation assays, which confirmed direct E2F1-PITX1 interactions. The probable binding sites for E2F1 in the PITX1 promoter were identified by DNA pulldown experiments. In silico and in vitro analyses show that the PITX1 proximal promoter region contains 2 specific sequences that are bound by E2F1. Overexpression of E2F1 enhances PITX1 promoter activity and mRNA transcription. In primary control and osteoarthritis chondrocytes, real time RT-PCR was used to measure the mRNA expression levels of candidate genes under E2F1 transcriptional control. Transcription Factor Dp-1 (TFDP1) knockdown experiments confirmed that the E2F1-TFDP1 complex regulates PITX1. Knockdown of TFDP1, an E2F1 dimerization partner, inhibits the activating effect of E2F1 and reduces both PITX1 promoter activity and mRNA transcription. Real time RT-PCR results reveal reduced expression of TFDP1 and a similar downregulation of their targets PITX1, BRCA1, CDKN1A, and RAD51 in mid-stage OA chondrocytes. Collectively, our data define a previously uncharacterized role for E2F1 and TFDP1 in the transcriptional regulation of PITX1 in articular chondrocytes. Additional E2F1 targets may be affected in OA pathogenesis.

Curcumin-Alleviated Osteoarthritic Progression in Rats Fed a High-Fat Diet by Inhibiting Apoptosis and Activating Autophagy via Modulation of MicroRNA-34a

“… 55 The E2F1-regulated protein PITX1 is an important regulatory factor whose inhibition can promote chondrocyte apoptosis. Pellicelli et al 20 demonstrated that inhibition of E2F1 suppressed PITX1 promoter activity and mRNA transcription in normal and OA articular chondrocytes. Downregulation of E2F1 has been associated with increased apoptosis of articular chondrocytes and OA deterioration, 56 , 57 while reduction of PITX1 synthesis and activity can lead to excessive lysis of chondrocytes, an important marker of articular cartilage degeneration.…”

“…The promoter activity and mRNA transcription of PITX1 (paired-like homeodomain transcription factor 1) have been shown to be regulated by E2F1 in OA chondrocytes. 20 However, the potential regulatory influences of miR-34a on E2F1, PITX1, and chondrocyte apoptosis remain to be explored.…”

Effects of caloric restriction on the antagonistic and integrative hallmarks of aging

“…Other than its function in cancer progression, induced levels of TFDP1 and its partner E2F were also observed in rat hippocampus after global cerebral ischemia together with its dimerization partner, the Rb binding protein, E2F1 (Jin et al, 2001). Lastly, knockdown of TFDP1 was found to reduce PITX1, whose loss of expression has been reported in patients suffering from osteoarthritis, a type of joint inflammation (Pellicelli et al, 2016).…”

Synovial Mesenchymal Stem Cell-Derived EV-Packaged miR-31 Downregulates Histone Demethylase KDM2A to Prevent Knee Osteoarthritis

“… 16 Meanwhile, E2F1 is involved in the regulation mechanism of OA. 17 However, there are few reports on whether KDM2A regulates E2F1 and participates in knee OA. This led us to explore the regulatory mechanism of KDM2A and E2F1 in knee OA.…”

“… 16 Interestingly, E2F1 has been implicated in the regulation mechanism of knee OA due to its potential in modulating articular chondrocytes. 17 Moreover, E2F1 can elevate the transcription of its downstream target gene, pituitary tumor transforming gene 1 (PTTG1), 18 which can promote OA progression. 19 Therefore, we aimed to delineate a hypothesized mechanism by which miR-31-mediated effects on the KDM2A/E2F1/PTTG1 axis exert regenerative effects on cartilage during OA.…”