Contents

1 Introduction

RTCGAToolbox primarily focuses on data management and download. We’ve kept the vignette section where the analysis functions are documented. Please contact the maintainer on GitHub, if you would like to create a package for the analysis functions and maintain them.

2 Post analysis functions

RTCGAToolbox has analyze functions to provide basic information about datasets. Analyze function includes differential gene expression analyze, correlation analysis between CN and GE data, univariate survival analysis, mutation frequency table and report figure.

2.1 Differential gene expression

RTCGAToolbox hires voom(Law, C. W. and Chen, Y. and Shi, W. and Smyth, G. K 2014) and limma(Smyth, G. K 2004) package functions to preform differential gene expression analysis between “Normal” and “Cancer” tissue samples. Every sample which is processed by TCGA project(Cancer Genome Atlas Research Network 2008) has a structured barcode number which includes the source of the tissue. RTCGAToolbox uses the barcode information to divide samples into “Normal” or “Tumor” groups and perform DGE analysis. Since “voom”(Law, C. W. and Chen, Y. and Shi, W. and Smyth, G. K 2014) requires raw count for RNASeq data, normalized RNASeq data cannot be used for the analysis. This function uses all gene expression datasets and returns a list which each member is “DGEResult” object. Each result object keeps top table from the genes that have 2 log fold change expression difference and significant adjusted p value. This function filters the results as a deafult behaviour using raw p value, adjusted p value and log fold change. Users can change “adj.pval”, “raw.pval” and “logFC” parameters to refine their results. Also function uses Benjamini & Hochberg adjustment for p values. For more details about adjment users can check base adjustment methods by calling “?p.adjust”. In addition to filter as a default behaviour function only draws heatmap for top 100 up and down regulated genes. Users can also adjust these values by using “hmTopUpN” and “hmTopDownN” parameters.

# Differential gene expression analysis for gene level RNA data.
diffGeneExprs <- getDiffExpressedGenes(dataObject=accmini, DrawPlots=TRUE,
    adj.method="BH", adj.pval=0.05, raw.pval=0.05, logFC=2, hmTopUpN=10,
    hmTopDownN=10)
# Show head for expression outputs
diffGeneExprs
showResults(diffGeneExprs[[1]])
toptableOut <- showResults(diffGeneExprs[[1]])

If “DrawPlots” set as FALSE, running code above won’t provide any output figure.

Voom + limma: To voom (variance modeling at the observational level) is to estimate the mean-variance relationship robustly and non-parametrically from the data. Voom works with log-counts that are normalized for sequence depth, in particular with log-counts per million (log-cpm). The mean-variance is fitted to the gene-wise standard deviations of the log-cpm, as a function of the average log-count. This method incorporates the mean-variance trend into a precision weight for each individual normalized observation. The normalized log-counts and associated precision weights can then be entered into the limma analysis pipeline, or indeed into any statistical pipeline for microarray data that is precision weight aware(Smyth, G. K 2004; Law, C. W. and Chen, Y. and Shi, W. and Smyth, G. K 2014). Users can check the following publications for more information about methods:

limma : Smyth, G. K. (2004). Linear models and empirical Bayes methods for assessing differential expression in microarray experiments. Statistical Applications in Genetics and Molecular Biology, Vol. 3, No. 1, Article 3.

Voom: Law, CW, Chen, Y, Shi, W, Smyth, GK (2014). Voom: precision weights unlock linear model analysis tools for RNA-seq read counts. Genome Biology15, R29.

2.2 Correlation between gene expression and copy number data

“getCNGECorrelation” function provides correlation coefficient and adjusted p value between copy number and gene expression data for each dataset. This function takes main dataobject as an input (uses gene copy number estimates from GISTIC2 (Mermel, C. H. and Schumacher, S. E. and Hill, B. and Meyerson, M. L. and Beroukhim, R. and Getz, G 2011) algorithm and gen expression values from every platform (RNAseq and arrays) to prepare return lists. List object stores “CorResult” object that contains results for each comparison.)

#Correlation between gene expression values and copy number
corrGECN <- getCNGECorrelation(dataObject=accmini, adj.method="BH",
    adj.pval=0.9, raw.pval=0.05)
corrGECN

If the dataset has RNASeq data, data will be normalized for correlation analysis. Correlation function uses Benjamini & Hochberg adjustment for p values. For more details about adjment users can check base adjustment methods by calling “?p.adjust”. In addition, to filter results adjusted and raw p values are used. Users can change “adj.pval” and “raw.pval” parameters to refine results.

The RTCGAToolbox uses one of Pearson’s product moment correlation coefficient to test for associations between paired samples. Measures of association, all in the range [-1, 1] with 0 indicating no association, shows how copy number alterations affect gene expression changes. The test statistic follows a t-distribution, with length (x)-2 degrees of freedom if the samples follow independent normal distributions. Users can get detailed information by calling ?cor.test function

2.3 Mutation frequencies

“getMutationRate” function gets the data frame that stores mutation frequency for the genes. This function gets the mutation information for each sample that has data and calculates frequency for each gene.

# Mutation frequencies
mutFrq <- getMutationRate(dataObject=accmini)
head(mutFrq[order(mutFrq[, 2], decreasing=TRUE), ])

3 Reproducing BRCA results from original manuscript

Following code block is provided to reproduce case study in the RTCGAToolbox paper(Samur MK. 2014).

# BRCA data with mRNA (Both array and RNASeq), GISTIC processed copy number data
# mutation data and clinical data
# (Depends on bandwidth this process may take long time)
brcaData <- getFirehoseData (dataset="BRCA", runDate="20140416",
    gistic2Date="20140115", clinic=TRUE, RNAseqGene=TRUE, mRNAArray=TRUE,
    Mutation=TRUE)

# Differential gene expression analysis for gene level RNA data.
# Heatmaps are given below.
diffGeneExprs <- getDiffExpressedGenes(dataObject=brcaData,DrawPlots=TRUE,
    adj.method="BH", adj.pval=0.05, raw.pval=0.05, logFC=2, hmTopUpN=100,
    hmTopDownN=100)
# Show head for expression outputs
diffGeneExprs
showResults(diffGeneExprs[[1]])
toptableOut <- showResults(diffGeneExprs[[1]])

# Correlation between expresiion profiles and copy number data
corrGECN <- getCNGECorrelation(dataObject=brcaData, adj.method="BH",
    adj.pval=0.05, raw.pval=0.05)

corrGECN
showResults(corrGECN[[1]])
corRes <- showResults(corrGECN[[1]])

# Gene mutation frequincies in BRCA dataset
mutFrq <- getMutationRate(dataObject=brcaData)
head(mutFrq[order(mutFrq[,2],decreasing=TRUE),])

# PIK3CA which is one of the most frequently mutated gene in BRCA dataset
# KM plot is given below.
clinicData <- getData(brcaData,"clinical")
head(clinicData)
clinicData <- clinicData[, 3:5]
clinicData[is.na(clinicData[, 3]), 3] <- clinicData[is.na(clinicData[, 3]), 2]
survData <- data.frame(Samples=rownames(clinicData),
    Time=as.numeric(clinicData[, 3]), Censor=as.numeric(clinicData[, 1]))
getSurvival(dataObject=brcaData, geneSymbols=c("PIK3CA"),
    sampleTimeCensor=survData)

Differentially expressed genes.