Functional exploration of the adult ovarian granulosa cell tumor-associated somatic FOXL2 mutation p.Cys134Trp (c.402C>G).
BACKGROUND
The somatic mutation in the FOXL2 gene c.402C>G (p.Cys134Trp) has recently been identified in the vast majority of adult ovarian granulosa cell tumors (OGCTs) studied. In addition, this mutation seems to be specific to adult OGCTs and is likely to be a driver of malignant transformation. However, its pathogenic mechanisms remain elusive.


RESULTS
We have sequenced the FOXL2 open reading frame in a panel of tumor cell lines (NCI-60, colorectal carcinoma cell lines, JEG-3, and KGN cells). We found the FOXL2 c.402C>G mutation in the adult OGCT-derived KGN cell line. All other cell lines analyzed were negative for the mutation. In order to gain insights into the pathogenic mechanism of the p.Cys134Trp mutation, the subcellular localization and mobility of the mutant protein were studied and found to be no different from those of the wild type (WT). Furthermore, its transactivation ability was in most cases similar to that of the WT protein, including in conditions of oxidative stress. A notable exception was an artificial promoter known to be coregulated by FOXL2 and Smad3, suggesting a potential modification of their interaction. We generated a 3D structural model of the p.Cys134Trp variant and our analysis suggests that homodimer formation might also be disturbed by the mutation.


CONCLUSIONS
Here, we confirm the specificity of the FOXL2 c.402C>G mutation in adult OGCTs and begin the exploration of its molecular significance. This is the first study demonstrating that the p.Cys134Trp mutant does not have a strong impact on FOXL2 localization, solubility, and transactivation abilities on a panel of proven target promoters, behaving neither as a dominant-negative nor as a loss-of-function mutation. Further studies are required to understand the specific molecular effects of this outstanding FOXL2 mutation.
Benayoun
Bérénice A
BA
Programme de Pathologie Moléculaire et Cellulaire, Institut Jacques Monod, Paris, France.
Caburet
Sandrine
S
Dipietromaria
Aurélie
A
Georges
Adrien
A
D'Haene
Barbara
B
Pandaranayaka
P J Eswari
PJ
L'Hôte
David
D
Todeschini
Anne-Laure
AL
Krishnaswamy
Sankaran
S
Fellous
Marc
M
De Baere
Elfride
E
Veitia
Reiner A
RA
D000328:Adult; D000595:Amino Acid Sequence; D045744:Cell Line, Tumor; D003545:Cysteine / Q000235:genetics*; D005260:Female; D000074842:Forkhead Box Protein L2; D051858:Forkhead Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D006106:Granulosa Cell Tumor / Q000235:genetics*; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D016366:Open Reading Frames; D010051:Ovarian Neoplasms / Q000235:genetics*; D013347:Subcellular Fractions / Q000378:metabolism; D015533:Transcriptional Activation; D014364:Tryptophan / Q000235:genetics*
C421604:FOXL2 protein, human; D000074842:Forkhead Box Protein L2; D051858:Forkhead Transcription Factors; D014364:Tryptophan; D003545:Cysteine