Introduction

This study aims to determine the role of stress-survival pathway (SSP) genes and the associated mutations in Hispanic colorectal cancer (CRC) disparities, particularly in young and late-stage Hispanic CRC. CRC is the second most-deadliest among all cancers and the third leading cause of cancer in the United States.  An overall reduction in CRC cases among individuals aged 50 and older has been reported, albeit there is an alarming rise in the incidence of early-onset (patients under 50) CRC. The increase in the early onset of CRC is concerning as these cases tend to appear with higher pathologic grades and have a higher risk of recurrence and metastasis. The incidence of early-onset CRC is almost two times in Hispanics (16.5%) compared to that in non-Hispanic White (NHWs; 8.7%). Access to health care for Hispanics is limited, as a result, they also tend to present with later-stage CRC when compared to NHWs (32% versus 19% of Stage IV), which likely accounts for their inferior age-adjusted survival after CRC diagnosis. Since Hispanics have the highest percentage of young people and comprise ~18% of the U.S. population, the rising incidence of early-onset and late-stage detection of CRC among Hispanics coupled with the rapid growth in this segment of the population makes it imperative to correctly assess the causes behind the observed disparities in Hispanics with early-onset and late-stage CRC. 

The risk of developing CRC is influenced by several modifiable and non-modifiable driving factors such as lifestyle factors, environment, intestinal microbiota, genetics, and age. These factors are also associated with the development of cellular oxidative stress that has been highly implicated in the initiation and progression of CRC. Several studies have shown oxidative stress and apoptosis as closely associated physiological phenomena that are highly incriminated in human colorectal tumorigenesis. Oxidative stress is the imbalance in the production of reactive oxygen species (ROS) and antioxidant defense, its role is not only limited to CRC development, but it is also well known for its interference in therapeutic interventions.

Methods

Our previous study, using in-silico analyses of CRC datasets, helped us identify twenty-eight oxidative stress-response and apoptosis-associated genes that expressed differently in CRC as compared to normal colon tissues. Expressions of these twenty-eight SSP genes (mRNA levels) were validated in six CRC cell lines using qRT-PCR. Stage-specific differential expressions were checked using cDNA arrays. Protein level expressions were analyzed using human colon cancer tissue microarrays (TMAs) by immunohistochemistry (IHC). Finally, we have confirmed the differential expression of all 28  transcripts in Hispanic and NHW CRC, and corresponding normal adjacent to the tumor (NAT) tissues by qRT-PCR. 

Results

Interestingly, we have identified distinct transcripts that are differentially expressed in Hispanics with early-onset (PDCD2L, CDK1, and PRDX4) and late-stage (CCNB1, CDK4, CHEK1, and MCM10) CRC. We have also identified the mutations associated with the SSP genes by analyzing datasets within the ClinVar and NHGRI-EBI GWAS databases. These findings have laid the foundation to characterize further, the roles played by these genes in the molecular basis for Hispanic CRC disparities at early-onset and late stages. Differential expression of mRNAs in CRC tissues between the two ethnic groups (Hispanics and NHW) and corresponding NATs has been determined by RNA-seq. Ingenuity Pathway Analysis (IPA) has been performed to correlate SSP genes with the canonical CRC pathways to better understand the roles played by these genes, their effects on the downstream cancer-related pathways, and on the early-onset and late-stage Hispanic CRC. 

Conclusion

These putative ethnicity-specific biomarkers or targets could be used for developing novel prognostic tools or therapeutic interventions for Hispanic CRC patients in the future.