EGFR/HER1 Isoforms Expression in Gliomas.
Angelique Guillaudeau, Helene Rabinovitch-Chable, Karine Durand, Sandrine Robert, Francois Labrousse. Dupuytren University Hospital, Limoges, France
Background: The EGFR gene encodes four different mRNAs generated by alternative splicing, the variants 1 to 4. Variant 1 mRNA generates the receptor isoform a, better known as EGFR or HER1, which consists of three domains, extracellular, trans-membrane and intracellular. Variants 2, 3 and 4 mRNAs respectively translate in isoforms b, c and d, three soluble receptors without intracellular domain. A mutant, EGFRvIII, have been reported in glioblastomas which differs from EGFR in a truncated extracellular domain. The role of the soluble receptors remains greatly unknown and their expression has never been studied in gliomas.
Design: EGFR variant 1, 2, 3 and 4 mRNAs were quantified by RT-PCR in 29 adult infiltrative gliomas (4 astrocytomas, 9 glioblastomas, 4 oligoastrocytomas and 12 oligodendrogliomas). Primer pairs were designed to amplify separately variant 2, 3 and 4 transcripts but variant 1 and EGFR vIII mRNAs together (variant 1+vIII). The relationship between variant mRNA levels and tumor types, EGFR gene amplification and EGFR protein expression detected by immunohistochemistry (IHC) was studied. For IHC analysis, we used two antibodies: one, targeted against the extracellular domains, bound the isoforms a, b, c, d and the EGFRvIII (Ext-Ab); the second one, targeted against the intracellular domain, labeled isoform a and EGFRvIII (Int-Ab). Immunoexpression was scored as no/weak for less than 50% of labeled tumor cells and strong for more than 50%.
Results: Transcripts of variants 1+vIII, 2, 3 and 4 were expressed in gliomas and their expression was strongly linked (p<0.0001). However, variants 3 and 4 were significantly overexpressed in glioblastomas (p=0.04 and p=0.03, respectively). Tumors with EGFR gene amplification expressed higher levels of variants 2, 3, and 4 transcripts (p=0.05, p=0.007 and p=0.02 respectively) than tumors without. The Ext-Ab labeled a higher number of tumor cells than the Int-Ab (p<0.0001). There was a positive correlation between variant 1+vIII mRNAs levels and EGFR protein expression detected with the Int-Ab (p=0.04). This link was not found with the Ext-Ab since it recognized the soluble isoforms in addition to isoforms a and mutant vIII.
Conclusions: EGFR/HER1 and EGFRvIII are not the sole isoforms expressed in gliomas. Other EGFR/HER1 variants, whose mRNAs encode soluble isoforms of the receptor, are strongly expressed in these tumors, notably in glioblastomas. Their expression should be taken into consideration when interpreting the results of the immunohistochemical analysis and to evaluate or seek treatments targeted against EGFR.
Tuesday, March 1, 2011 1:00 PM
Platform Session: Section G, Tuesday Afternoon