2.1 Genetic alterations and expression analysis of PCAT1 gene in multiple cancers: We used cBioportal to study genetic alteration of PCAT1. The PCAT1 had genetically altered in 13.38% of IBC patients when investigated through pancancer atlas dataset of 32 different cancers (Fig. 2A). A significant copy number alteration (CNA) i.e., amplification has noticed throughout different cancers data set. We have further utilized GEPIA to explore the transcriptional expression of PCAT1 in BARCA mutated BC patients. Data revealed that PCAT1 highly expressed (1.56-fold; BRCA- 0.14, normal cell- 0.09) compared to normal cells (Fig. 2 B). Based on these findings we considered PCAT1 gene for our analysis in IBC.
2.2 Genetic alteration of PCAT1 in IBC: We explored 12 studies (4807 samples) (Fig. 3A) of IBC of cBioportal which were CPTAC (41), METABRIC (42), Provisional (43), TCGA (44), INSERM (45), MSK (46), SMC 2018 (47), British Columbia (48), MSKCC (49), British Columbia (50), Broad (51), and Sanger (52) to figure out the percentage of patient having PCAT1 alteration. We found that (Fig. 3A), PCAT1 amplified in considerable number of patients in first 5 studies which were 35.25%, 24.44%, 21.52%, 19.29%, and 17.5% respectively. Besides, in Oncoprint data of 12 studies, (Fig. 3B) PCAT1 gene showed amplification in 20% of IBC patients. Among first 5 studies of (Fig. 3A), we considered 2 studies i.e., METABRIC (42) and CPTAC (41) (2,631 samples) where patients were diagnosed for primary BC (42) (41). Besides, we investigated INSERM (45) data which considered only metastatic tumor (45). Therefore, we intended to find out the genetic alteration, survival rate, clinical outcomes, and tendency of co-occurrence of PCAT1 with other oncogenes in patients with primary and metastatic BC.
2.3 PCAT1 gene mainly amplified in primary and metastatic BC: It was observed that, according to the CPTAC (41), and METABRIC (42) the PCAT1 gene experienced amplification in 35% (Fig. 4A) and 24% (Fig. 4B) of primary BC patients respectively. On top of that, considering these 2 studies (Fig. 4C) at a time we found amplification of PCAT1 in 25% of patients. Besides, 18% of metastatic BC patients showed amplification (Fig. 4D) during analyzing the INSERM (45) data set. Besides the Z-score of mRNA expression data (Fig. 4E) represented significant (p- 1.717e-3) relation with CNA of PCAT1 from CPTAC (41), and METABRIC (42). Moreover, INSERIM (45) data represented the CNA of PCAT1 among patients with metastatic BC (Fig: 4F).
2.4 Survival rate decreased in patients, diagnosed for primary BC, with PCAT1 gene alteration: The patients who were suffering from primary BC with amplified PCAT1 gene had median survival of 132.33 months (p value 5.539e-5) as compared to median survival (167.93 months) of patients without PCAT1 alteration (Fig. 5A). This data indicates that the amplification of PCAT1 significantly reduced the overall survival rate of patients with primary BC. From Kaplan–Meier plot, we also found the downward trend of survival rate with progression of months while PCAT1 overexpressed (Fig. 5B). However, the survival rate in case of metastatic BC was not investigated in INSERM (45) data set.
2.5 PCAT1 gene expression is related with ER, PR, and HER2 expression of patients: When we explored the clinical attributes from cBioportal we figured out that the PCAT1 significantly altered in PR (p- 1.672e-6) and HER2 (p-3.190 e-6) negative as well as ER (p- 3.920e-4) positive primary BC samples (Fig. 6A-6C). However, these clinical attributes, in case of metastatic tumor, were not present in INSERM Cancer (45) dataset. After understanding the relation of PCAT1 expression which co-occurs significantly (p- <0.001) with Estrogen Receptor 1 (ESR1) (Fig. 6D), we then intended to check how this lncRNA related with patient age and histologic grade.
2.6 PCAT1 did not correlated with patient age while showed positive correlation with Neoplasm histologic grade of tumor: While investigation of the primary BC data set was conducted using cBioportal, there is no significant correlation of PCAT1 expression with patient age was detected (Fig. 7A). However, this relation was not evaluated in INSERM (45) dataset. In addition, we analyzed the correlation between the PCAT1 expressions with neoplasm histologic grade 1, 2 and 3 which can differentiate between normal and cancerous cells. Moreover, it is also found that, in primary BC samples with different grade of tumor, the PCAT1 amplified significantly (68.42%, p- >10-10) in grade 3 cancer compared to grade 2 and 1 tumor (28.85% and 2.73% expression, respectively; Fig. 7B). These results indicated that the PCAT1 gene altered mostly in the grade 3 histological grade of cancer cells (Fig. 7C-7F). We also investigated the relation of ER expression with neoplastic histologic grade of primary BC from CPTAC (41) and METABRIC (42). Our findings showed that, in primary BC samples with grade 3, 2 and 1 tumor, the ESR1 amplified significantly (p- 1.985 e-3) in 45.08 %, 37.40% and 7.77 % samples respectively (Fig. 7G). These results indicated that, as like PCAT1, ER also altered in the highest percentage in samples with grade 3 cancer cells. This finding supported the notion of the co-occurrence of PCAT1 and ER in IBC.
2.7 PCAT1 gene amplification co-occurs with CASC8, CASC11, and CASC19 oncogenes: To find out the co-occurrence of PCAT1 expression with other oncogenes, we analyzed the cBioportal for the genes of highest genetic alteration (considering genes with most significant p value) in primary and metastatic BC patients. Our finding demonstrated that CASC8 altered in both primary and metastatic BC patients (~100%) (Fig. 8A, Fig. 8B). Besides in primary BC patients the anther two sub-groups of CASC family (CASC11 and CASC19) showed the highest alteration (100%). Moreover, genetic amplification of PCAT1 (25%), CASC8 (26%), CASC11 (24%), and CASC19 (23%) was observed from OncoPrint with the same data set of primary BC (Figure 9A). Similarly, we explored alteration of CASC8 (Fig. 9B) for metastatic cancer patients where the percentage for PCAT1 and CASC8 was 18% and 19% respectively. Concurrent genetic alteration of genes indicates that they may come up with the distinctive cancer subtypes (11). To identify mutual exclusivity and co-occurrence of CASC subfamily (CASC8, CASC11 and CASC19) and PCAT1 gene we queried the same data set of primary and metastatic BC from cBioportal. CASC8, CASC11 and CASC19 are previously known to have relation with BC as well as works as biomarker for different types of cancers including colorectal, esophageal (53)(54)(55)(56).The CASC8, CASC11, and CASC19 significantly (p- < 0.001) co-occurred with PCAT1 (Fig. 9C) in primary BC. Likely, the CASC8 co-occurs significantly (p value < 0.001) with PCAT1 in metastatic BC (Fig. 9D). In addition, we investigated the overall survival of primary BC patients with concurrent alteration in PCAT1, CASC8, CASC11, and CASC19 (Fig. 9E). The patients with alteration of these genes (Fig. 9E) have median survival of 125.60 months (p- 5.8e-6) as compared to median survival (168.97 months) of patients without alteration of genes. Therefore, this data indicated that the co-occurring alteration of PCAT1 with CASC8, CASC11, and CASC19 significantly reduced the overall survival rate of patients with BC.
To figure out the genome location of PCAT1, CASC8, CASC11, and CASC19 we used the Integrative Genomics Viewer (IGV) data (Fig. 10A-10D) and found that these were located in same chromosome (chr8q24) which is known to have BC risk region (57). Besides, we queried the Ensembl data, where we extracted a graph for PCAT1 location which indicates the overlapping tendency of PCAT1 with CASC8 and CASC19 together (Fig. 10E). Moreover, ENCOR data set (https://starbase.sysu.edu.cn/) was used for the analysis of the co-expression of PCAT1 with CASC8, CASC11, and CASC19. The finding represented the significant co-expression of PCAT1 with CASC8 (Fig. 11A, p value 1.04e-19), CASC11 (Fig. 11B; p- 4.57e-17), and CASC19 (Fig. 10C, p value 8.91e-44). These investigations concluded an interesting result of co-occurrence of PCAT1 with other three oncogenes and biomarker of cancers (CASC8, CASC11, and CASC19). So, the PCAT1 has the highest possibility to act as prognostic biomarker in IBC.