High prevalence of chromosome 17 in breast cancer micronuclei: a means to get rid of tumor suppressors?

Micronuclei (MN), defined as small extra-nuclear chromatin bodies enclosed by a nuclear envelope, serve as noticeable markers of chromosomal instability (CIN). The MN have been used for breast cancer (BC) screening, diagnosis, and prognosis. However, more recently they have gained attention as seats for active chromosomal rearrangements. BC subtypes exhibit differential CIN levels and aggressiveness. This study aimed to investigate MN chromosomal contents across BC subtypes, exploring its potential role in aggressiveness and pathogenesis. Immunostaining of BC cells was performed with anti-centromeric antibody followed by confocal microscopy. Further, fluorescence in situ hybridization (FISH) was done to check the presence of specific chromosomes in the MN. The real time PCR was also done from the RNA isolated from MN to check the expression of TP53 gene. BC cell lines (CLs) showed the presence of both centromere-positive ( +) and -negative ( -) MN, with significant variation in frequency among hormone and human epidermal growth factor receptor positive and triple-negative (TN) BC cells. FISH targeting chromosomes 1, 3, 8, 11, and 17 detected centromeric signals for all the above chromosomes in MN with a relatively higher prevalence of chromosome 17 in all the CLs. Out of all the CLs, TNBC cells demonstrated the highest frequency of centromere + and chromosome 17 + MN. TP53 expression could also be demonstrated inside the MN by FISH and real time PCR. Patient sample imprints also confirmed the presence of chromosome 17 in MN with polysomy of the same in corresponding nuclei. The high prevalence of chromosome 17 in BC MN may connote the importance of its rearrangements in the pathogenesis of BC. Further, the higher prevalence of chromosome 17 and 1 signals in TNBC MN point towards the significance of pathogenetic events involving the genes located in these chromosomes in evolution of this more aggressive phenotype.