In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Furthermore , activation or overexpression of Nrf2 inhibited the promoter activity of TGF - beta1 in a dose - dependent manner , whereas knockdown of Nrf2 by siRNA enhanced TGF - beta1 transcription and fibronectin production .
### Output Text:
Furthermore , activation or overexpression of Nrf2 inhibited the promoter activity of TGF - beta1 in a dose - dependent manner , whereas knockdown of Nrf2 by siRNA enhanced TGF - beta1 transcription and fibronectin production . 