HER family members contribute to onset of resistance to PHA treatment. (A) Cell viability of GTL16 cells resistant to 500 nM PHA (GTL16 R500) compared to wt cells, grown in the presence of the drug for 96 hours. Growth of GTL16 R500 was not affected by the PHA. (B) Expression levels of HER family members in GTL16 cells wt or resistant to PHA, evaluated by Real time PCR. Absolute values were normalized to GAPDH. (C) Cell viability upon silencing of HER2/HER3. In GTL16 cells expression of HER2 and HER3 was silenced. While the silencing of the two receptors did not affect viability of wt cells, in GTL16 R500 the absence of HER2 and HER3 resulted in increased sensibility to PHA (*** P < 0,001).