11. When HeLa cells were treated with the growth factor TGF-β for 30 minutes, levels of
E-Cadherin protein were reduced. mRNA levels of the E-Cadherin gene (CDH1) did not
show any reduction. What could be the potential mechanism behind this observation?
a. Inhibition of translation of CDH1 mRNA
b. Degradation of E-Cadherin protein
c. Increased stability of CDH1 mRNA
d. Both ‘a’ and ‘b’

TGF-β treatment reduces E-Cadherin protein levels in HeLa cells within 30 minutes without affecting CDH1 mRNA, indicating a post-transcriptional mechanism. This observation aligns with rapid TGF-β signaling disrupting epithelial integrity during early epithelial-mesenchymal transition (EMT). The correct answer is d. Both ‘a’ and ‘b’, as both translation inhibition and protein degradation contribute.​

Option Analysis

a. Inhibition of translation of CDH1 mRNA
TGF-β rapidly activates non-Smad pathways like Akt and PAK1, phosphorylating RNA-binding proteins such as hnRNP E1. This releases translational repression on certain transcripts but can inhibit CDH1 mRNA translation via altered ribosome loading or microRNA interactions, reducing protein synthesis without mRNA decay. This fits the 30-minute timeframe, as transcriptional changes take longer.​

b. Degradation of E-Cadherin protein
TGF-β triggers endocytosis of E-Cadherin from cell junctions via phosphorylation of β-catenin and activation of RhoA or Src kinases, leading to lysosomal or proteasomal degradation. Studies confirm TGF-β promotes clathrin-mediated endocytosis and ubiquitinylation of existing E-Cadherin protein, causing rapid loss independent of new synthesis. No mRNA change supports this post-translational effect.​

c. Increased stability of CDH1 mRNA
This option contradicts the observation, as increased mRNA stability would elevate CDH1 transcripts or maintain protein levels. TGF-β typically destabilizes epithelial mRNAs during EMT via miRNAs or deadenylation, but here mRNA levels remain unchanged, ruling out this mechanism.​

d. Both ‘a’ and ‘b’
Both post-transcriptional processes occur: translation block prevents new protein, while degradation clears existing E-Cadherin. Rapid kinetics (30 minutes) match combined effects seen in HeLa EMT models, where TGF-β disrupts adhesion before transcriptional repression dominates.​

Biological Context

TGF-β signaling in HeLa cells initiates via receptor phosphorylation, activating Smads for transcription alongside fast non-canonical paths like MAPK and PI3K. E-Cadherin loss disrupts adherens junctions, promoting motility key to cancer metastasis. For CSIR NET, recognize that unchanged mRNA points to translation/degradation over repression by Snail/ZEB factors, which reduce transcripts after hours.​

Exam Relevance