bp: A Best Practice for Signature Extraction and Exposure...

In sigminer: Extract, Analyze and Visualize Mutational Signatures for Genomic Variations

A Best Practice for Signature Extraction and Exposure (Activity) Attribution

Description

These functions are combined to provide a best practice for optimally identifying mutational signatures and attributing their activities (exposures) in tumor samples. They are listed in order to use.

• bp_extract_signatures() for extracting signatures.

• bp_show_survey() for showing measures change under different signature numbers to help user select optimal signature number. At default, an aggregated score (named score) is generated to suggest the best solution.

• bp_show_survey2() for showing simplified signature number survey like show_sig_number_survey().

• bp_get_sig_obj() for get a (list of) Signature object which is common used in sigminer for analysis and visualization.

• bp_attribute_activity() for optimizing signature activities (exposures). NOTE: the activities from extraction step may be better! You can also use sig_extract to get optimal NMF result from multiple NMF runs. Besides, you can use sig_fit to quantify exposures based on signatures extracted from bp_extract_signatures().

• bp_extract_signatures_iter() for extracting signature in a iteration way.

• bp_cluster_iter_list() for clustering (hclust with average linkage) iterated signatures to help collapse multiple signatures into one. The result cluster can be visualized by plot() or factoextra::fviz_dend().

• bp_get_clustered_sigs() for getting clustered (grouped) mean signatures from signature clusters.

• Extra: bp_get_stats() for obtaining stats for signatures and samples of a solution. These stats are aggregated (averaged) as the stats for a solution (specific signature number).

• Extra: bp_get_rank_score() for obtaining rank score for all signature numbers.

Usage

bp_extract_signatures(
  nmf_matrix,
  range = 2:5,
  n_bootstrap = 20L,
  n_nmf_run = 50,
  RTOL = 0.001,
  min_contribution = 0,
  cores = min(4L, future::availableCores()),
  cores_solution = min(cores, length(range)),
  seed = 123456L,
  handle_hyper_mutation = TRUE,
  report_integer_exposure = FALSE,
  only_core_stats = nrow(nmf_matrix) > 100,
  cache_dir = file.path(tempdir(), "sigminer_bp"),
  keep_cache = FALSE,
  pynmf = FALSE,
  use_conda = TRUE,
  py_path = "/Users/wsx/anaconda3/bin/python"
)

bp_extract_signatures_iter(
  nmf_matrix,
  range = 2:5,
  sim_threshold = 0.95,
  max_iter = 10L,
  n_bootstrap = 20L,
  n_nmf_run = 50,
  RTOL = 0.001,
  min_contribution = 0,
  cores = min(4L, future::availableCores()),
  cores_solution = min(cores, length(range)),
  seed = 123456L,
  handle_hyper_mutation = TRUE,
  report_integer_exposure = FALSE,
  only_core_stats = nrow(nmf_matrix) > 100,
  cache_dir = file.path(tempdir(), "sigminer_bp"),
  keep_cache = FALSE,
  pynmf = FALSE,
  use_conda = FALSE,
  py_path = "/Users/wsx/anaconda3/bin/python"
)

bp_cluster_iter_list(x, k = NULL, include_final_iteration = TRUE)

bp_get_clustered_sigs(SigClusters, cluster_label)

bp_get_sig_obj(obj, signum = NULL)

bp_get_stats(obj)

bp_get_rank_score(obj)

bp_show_survey2(
  obj,
  x = "signature_number",
  left_y = "silhouette",
  right_y = "L2_error",
  left_name = left_y,
  right_name = right_y,
  left_color = "black",
  right_color = "red",
  left_shape = 16,
  right_shape = 18,
  shape_size = 4,
  highlight = NULL
)

bp_show_survey(
  obj,
  add_score = FALSE,
  scales = c("free_y", "free"),
  fixed_ratio = TRUE
)

bp_attribute_activity(
  input,
  sample_class = NULL,
  nmf_matrix = NULL,
  method = c("bt", "stepwise"),
  bt_use_prop = FALSE,
  return_class = c("matrix", "data.table"),
  use_parallel = FALSE,
  cache_dir = file.path(tempdir(), "sigminer_attribute_activity"),
  keep_cache = FALSE
)

Arguments

nmf_matrix	a matrix used for NMF decomposition with rows indicate samples and columns indicate components.
range	a numeric vector containing the ranks of factorization to try. Note that duplicates are removed and values are sorted in increasing order. The results are notably returned in this order.
n_bootstrap	number of bootstrapped (resampling) catalogs used. When it is 0, the original (input) mutation catalog is used for NMF decomposition, this is not recommended, just for testing, user should not set it to 0.
n_nmf_run	number of NMF runs for each bootstrapped or original catalog. At default, in total n_bootstrap x n_nmf_run (i.e. 1000) NMF runs are used for the task.
RTOL	a threshold proposed by Nature Cancer paper to control how to filter solutions of NMF. Default is ⁠0.1%⁠ (from reference #2), only NMF solutions with KLD (KL deviance) <= ⁠100.1%⁠ minimal KLD are kept.
min_contribution	a component contribution threshold to filer out small contributed components.
cores	number of cpu cores to run NMF.
cores_solution	cores for processing solutions, default is equal to argument cores.
seed	a random seed to make reproducible result.
handle_hyper_mutation	default is TRUE, handle hyper-mutant samples.
report_integer_exposure	if TRUE, report integer signature exposure by bootstrapping technique.
only_core_stats	if TRUE, only calculate the core stats for signatures and samples.
cache_dir	a directory for keep temp result files.
keep_cache	if TRUE, keep cache results.
pynmf	if TRUE, use Python NMF driver Nimfa. The seed currently is not used by this implementation, so the only way to reproduce your result is setting keep_cache = TRUE.
use_conda	if TRUE, create an independent conda environment to run NMF.
py_path	path to Python executable file, e.g. '/Users/wsx/anaconda3/bin/python'. In my test, it is more stable than use_conda=TRUE. You can install the Nimfa package by yourself or set use_conda to TRUE to install required Python environment, and then set this option.
sim_threshold	a similarity threshold for selecting samples to auto-rerun the extraction procedure (i.e. bp_extract_signatures()), default is 0.95.
max_iter	the maximum iteration size, default is 10, i.e., at most run the extraction procedure 10 times.
x	result from bp_extract_signatures_iter() or a list of Signature objects.
k	an integer sequence specifying the cluster number to get silhouette.
include_final_iteration	if FALSE, exclude final iteration result from clustering for input from bp_extract_signatures_iter(), not applied if input is a list of Signature objects.
SigClusters	result from bp_cluster_iter_list().
cluster_label	cluster labels for a specified cluster number, obtain it from SigClusters$sil_df.
obj	a ExtractionResult object from bp_extract_signatures().
signum	a integer vector to extract the corresponding Signature object(s). If it is NULL (default), all will be returned.
left_y	column name for left y axis.
right_y	column name for right y axis.
left_name	label name for left y axis.
right_name	label name for right y axis.
left_color	color for left axis.
right_color	color for right axis.
left_shape, right_shape, shape_size	shape setting.
highlight	a integer to highlight a x.
add_score	if FALSE, don't show score and label optimal points by rank score.
scales	one of "free_y" (default) and "free" to control the scales of plot facet.
fixed_ratio	if TRUE (default), make the x/y axis ratio fixed.
input	result from bp_extract_signatures() or a Signature object.
sample_class	a named string vector whose names are sample names and values are class labels (i.e. cancer subtype). If it is NULL (the default), treat all samples as one group.
method	one of 'bt' (use bootstrap exposure median, from reference #2, the most recommended way in my personal view) or stepwise' (stepwise reduce and update signatures then do signature fitting with last signature sets, from reference #2, the result tends to assign the contribution of removed signatures to the remaining signatures, maybe I misunderstand the paper method? PAY ATTENTION).
bt_use_prop	this parameter is only used for bt method to reset low contributing signature activity (relative activity ⁠<0.01⁠). If TRUE, use empirical P value calculation way (i.e. proportion, used by reference ⁠#2⁠), otherwise a t.test is applied.
return_class	string, 'matrix' or 'data.table'.
use_parallel	if TRUE, use parallel computation based on furrr package. It can also be an integer for specifying cores.

Details

The signature extraction approach is adopted from reference #1, #2, and the whole best practice is adopted from the pipeline used by reference #3. I implement the whole procedure with R code based on the method description of papers. The code is well organized, tested and documented so user will find it pretty simple and useful. Besides, the structure of the results is very clear to see and also visualize like other approaches provided by sigminer.

Value

It depends on the called function.

Measure Explanation in Survey Plot

The survey plot provides a pretty good way to facilitate the signature number selection. A score measure is calculated as the weighted mean of selected measures and visualized as the first sub-plot. The optimal number is highlighted with red color dot and the best values for each measures are also highlighted with orange color dots. The detail of 6 measures shown in plot are explained as below.

• score - an aggregated score based on rank scores from selected measures below. The higher, the better. When two signature numbers have the same score, the larger signature number is preferred (this is a rare situation, you have to double check other measures).

• silhouette - the average silhouette width for signatures, also named as ASW in reference #2. The signature number with silhouette decreases sharply is preferred.

• distance - the average sample reconstructed cosine distance, the lower value is better.

• error - the average sample reconstructed error calculated with L2 formula (i.e. L2 error). This lower value is better. This measure represents a similar concept like distance above, they are all used to quantify how well sample mutation profiles can be reconstructed from signatures, but distance cares the whole mutation profile similarity while error here cares value difference.

• ⁠pos cor⁠ - the average positive signature exposure correlation coefficient. The lower value is better. This measure is constructed based on my understanding about signatures: mutational signatures are typically treated as independent recurrent patterns, so their activities are less correlated.

• similarity - the average similarity within in a signature cluster. Like silhouette, the point decreases sharply is preferred. In the practice, results from multiple NMF runs are clustered with "clustering with match" algorithm proposed by reference #2. This value indicates if the signature profiles extracted from different NMF runs are similar.

Author(s)

Shixiang Wang [e-mail]

References

Alexandrov, Ludmil B., et al. "Deciphering signatures of mutational processes operative in human cancer." Cell reports 3.1 (2013): 246-259.

Degasperi, Andrea, et al. "A practical framework and online tool for mutational signature analyses show intertissue variation and driver dependencies." Nature cancer 1.2 (2020): 249-263.

Alexandrov, Ludmil B., et al. “The repertoire of mutational signatures in human cancer.” Nature 578.7793 (2020): 94-101.

See Also

See sig_estimate, sig_extract, sig_auto_extract, sigprofiler_extract for other approaches.

Examples

data("simulated_catalogs")

# Here I reduce the values for n_bootstrap and n_nmf_run
# for reducing the run time.
# In practice, you should keep default or increase the values
# for better estimation.
#
# The input data here is simulated from 10 mutational signatures

# e1 <- bp_extract_signatures(
#   t(simulated_catalogs$set1),
#   range = 8:12,
#   n_bootstrap = 5,
#   n_nmf_run = 10
# )
#
# To avoid computation in examples,
# Here just load the result
# (e1$signature and e1$exposure set to NA to reduce package size)
load(system.file("extdata", "e1.RData", package = "sigminer"))


# See the survey for different signature numbers
# The suggested solution is marked as red dot
# with highest integrated score.
p1 <- bp_show_survey(e1)
p1
# You can also exclude plotting and highlighting the score
p2 <- bp_show_survey(e1, add_score = FALSE)
p2

# You can also plot a simplified version
p3 <- bp_show_survey2(e1, highlight = 10)
p3

# Obtain the suggested solution from extraction result
obj_suggested <- bp_get_sig_obj(e1, e1$suggested)
obj_suggested
# If you think the suggested signature number is not right
# Just pick up the solution you want
obj_s8 <- bp_get_sig_obj(e1, 8)

# Track the reconstructed profile similarity
rec_sim <- get_sig_rec_similarity(obj_s8, t(simulated_catalogs$set1))
rec_sim

# After extraction, you can assign the signatures
# to reference COSMIC signatures
# More see ?get_sig_similarity
sim <- get_sig_similarity(obj_suggested)
# Visualize the match result
if (require(pheatmap)) {
  pheatmap::pheatmap(sim$similarity)
}

# You already got the activities of signatures
# in obj_suggested, however, you can still
# try to optimize the result.
# NOTE: the optimization step may not truly optimize the result!
expo <- bp_attribute_activity(e1, return_class = "data.table")
expo$abs_activity


## Not run: 
# Iterative extraction:
# This procedure will rerun extraction step
# for those samples with reconstructed catalog similarity
# lower than a threshold (default is 0.95)
e2 <- bp_extract_signatures_iter(
  t(simulated_catalogs$set1),
  range = 9:11,
  n_bootstrap = 5,
  n_nmf_run = 5,
  sim_threshold = 0.99
)
e2
# When the procedure run multiple rounds
# you can cluster the signatures from different rounds by
# the following command
# bp_cluster_iter_list(e2)

## Extra utilities
rank_score <- bp_get_rank_score(e1)
rank_score
stats <- bp_get_stats(e2$iter1)
# Get the mean reconstructed similarity
1 - stats$stats_sample$cosine_distance_mean

## End(Not run)

sigminer documentation built on Aug. 21, 2023, 9:08 a.m.