Consistent with the finding noted by p120 siRNA in our previous report,
18 p120-Kaiso siRNAs triggered nuclear translocation of p120 and nuclear colocalization of BrdU (
Fig. 4C), indicating that p120-Kaiso siRNAs also unlocked the mitotic block in the contact-inhibited HCEC monolayer. Herein, we noted that nuclear localization of pNFκB (p65), p120, and BrdU was also aborted by simultaneous addition for 2 days of noggin, an extracellular BMP inhibitor,
26 and 5Z-7-Oxozeaenol, a small molecular weight inhibitor of the mitogen-activated protein kinase kinase kinase TAK1,
27 which is involved in noncanonical BMP signaling to generate pNFκB.
28–30 Thus, we investigated whether knockdown by p120-Kaiso siRNAs elicited BMP signaling. Quantitative RT-PCR analyses revealed upregulation of BMP2, BMP4, and BMPR1B transcripts by both p120 siRNA and p120-Kaiso siRNAs, with the latter more so than the former, when compared with the corresponding scRNA control (
Fig. 5A, *
P < 0.05 and **
P < 0.01) However, transcript expression of ID1, ID, ID3, and ID4 was not affected (
Fig. 5B, all
P > 0.05) and nuclear staining of pSMAD1/5/8 was not observed by knockdown with both p120 siRNA and p120-Kaiso siRNAs (
Fig. 5C), suggesting that the canonical BMP signaling was not activated. Upregulation of BMP2, BMP4, and BMPR1B was markedly attenuated by the Rho inhibitor CT-04 and to a lesser extent by the ROCK inhibitor Y27632, NFkB inhibitor CAY10512, the BMP inhibitor noggin, and the TAK1 inhibitor 5Z-7-Oxozeaenol (
Fig. 5D, all
P < 0.05). The downregulation of BMP4 and BMPR1A transcript by CT-04 was even less than the control level achieved by scRNA (
Fig. 5D,
P < 0.05). These results collectively suggested that the signaling of RhoA activation triggered by knockdown with p120-Kaiso siRNAs led to downstream noncanonical BMP signaling to generate nuclear translocation of pNFκB and colocalization of p120 and BrdU.