Secreted Wnt6 mediates diabetes-associated centrosome amplification via its receptor FZD4.

We recently published that type 2 diabetes promotes cell centrosome amplification via upregulation of Rho-associated protein kinase 1 (ROCK1) and 14-3-3 protein-σ (14-3-3σ). This study further investigates the molecular mechanisms underlying diabetes-associated centrosome amplification. We found that treatment of cells with high glucose, insulin, and palmitic acid levels increased the intracellular and extracellular protein levels of Wingless-type MMTV integration site family member 6 (Wnt6) as well as the cellular level of ß-catenin. The treatment also activated ß-catenin and promoted its nuclear translocation. Treatment of cells with siRNA species for Wnt6, Frizzled-4 (FZD4), or ß-catenin as well as introduction of antibodies against Wnt6 or FZD4 to the cell culture medium could all attenuate the treatment-triggered centrosome amplification. Moreover, we showed that secreted Wnt6-FZD4-ß-catenin was the signaling pathway that was upstream of ROCK1 and 14-3-3σ. We found that advanced glycation end products (AGEs) were also able to increase the cellular and extracellular levels of Wnt6, the cellular protein level of ß-catenin, and centrosome amplification. Treatment of the cells with siRNA species for Wnt6 or FZD4 as well as introduction of antibodies against Wnt6 or FZD4 to the cell culture could all inhibit the AGEs-elicited centrosome amplification. In colon tissues from a diabetic mouse model, the protein levels of Wnt6 and 14-3-3σ were increased. In conclusion, our results showed that the pathophysiological factors in type 2 diabetes, including AGEs, were able to induce centrosome amplification. It is suggested that secreted Wnt6 binds to FZD4 to activate the canonical Wnt6 signaling pathway, which is upstream of ROCK1 and 14-3-3σ, and that this is the cell signaling pathway underlying diabetes-associated centrosome amplification.

PPARγ promotes diabetes-associated centrosome amplification via increasing the expression of SKA1 directly at the transcriptional level.

We have recently published that type 2 diabetes can induce cell centrosome amplification due to the action of high glucose, palmitic acid, and insulin, and ROCK1 and 14-3-3σ are signal mediators. In this study, we further investigated the molecular mechanisms of the centrosome amplification in colon cancer HCT116 cells. Treatment of the cells with high glucose, palmitic acid, and insulin increased the expression of peroxisome proliferator-activated receptor γ (PPARγ) as well as the spindle and kinetochore associated protein 1 (SKA1), knockdown of each of which resulted in the inhibition of the treatment-triggered centrosome amplification. Knockdown of PPARγ inhibited the treatment-evoked increase in the SKA1 level, whereas knockdown of SKA1 did not modify the treatment-increased PPARγ level. We found a predicted binding site for PPARγ in the promoter region of the SKA1 gene from the JASPAR database. Experimental results showed that the treatment increased the messenger RNA level of SKA1, which could be inhibited by PPARγ chemical inhibitor or small interfering RNA. Moreover, we were able to show that PPARγ could bind to the binding site in the SKA1 gene promoter, which was increased by the experimental treatment. In conclusion, it is suggested that the pathophysiological factors in type 2 diabetes, high glucose, palmitic acid, and insulin, induce the cell centrosome amplification through the PPARγ-SKA1 pathway, in which PPARγ increases the expression of SKA1 via directly enhancing the SKA1 gene transcription.