[Abnormality of anaplastic lymphoma kinase gene and its expression in pediatric neuroblastoma]

To correlate the abnormal expression of anapastic lymphoma kinase (ALK) protein with the genetic and epigenetic changes of ALK, and to analyze its clinical application in pediatric neuroblastoma.

Three neuroblastoma (NB) cell lines (two ALK positive: SH-SY5Y and SK-N-SH, one ALK negative: SK-N-AS) and 43 paraffin-embedded NB tissues were included in the study. In both cell lines and clinical cases, immunohistochemistry was used to detect ALK protein expression; PCR and Sanger sequencing were used to detect ALK point mutation; fluorescence in situ hybridization (FISH) was used to detect ALK abnormality and bisulfite sequencing PCR (BSP) was used to detect methylation of CpG island in the promoter area of ALK.

The cell lines SH-SY5Y and SK-N-SH were positive for ALK expression (cytoplasm), while the SK-N-AS was negative; among the 43 cases of NB, 26 (60.5%, 26/43) were positive for ALK protein (membrane and cytoplasm), and the rest were negative. Survival analysis showed ALK protein expression was related to survival time, with ALK positive cases having shorter survival time than ALK negative cases (P = 0.020). But ALK protein expression had no association with tumor differentiation (P = 0.503), tumor sites (P = 1.000) and age of patients (P = 0.063). FISH showed ALK amplification in two cases (4.6%, 2/43), ALK gain was found in 30 cases (69.7%, 30/43), and the remaining cases had normal ALK copy (25.6%, 11/43). The presence of extra copies (amplification and gain) of ALK was associated with ALK positive protein expression (P = 0.020), but there was no association with tumor differentiation (P = 1.000), tumor sites (P = 0.775) and age of patients (P = 0.328). No point mutation was found in all three cell lines. Of the 43 NB cases, only one case (2.3%, 1/43) showed point mutation in exon 23, and was a synonymous mutation [A1200A (G4552C)]. The case was ALK negative, but the patient died two months after diagnosis. BSP analysis showed that CpG island in ALK promoter region were all unmethylated in three cell lines and 6 NB cases (including 3 ALK positive, 3 ALK negative).

ALK protein is expressed in most NB, and the expression indicates poor outcome. ALK expression is associated with extra copies of ALK, but there is no association with the methylation status of CpG island of ALK; the presence of extra copies of ALK is the most common genetic aberration in NB. Point mutation of ALK is rare, and may predict poor prognosis in pediatric NB.