Single-cell transcriptomes underscore genetically distinct tumor characteristics and microenvironment for hereditary kidney cancers

A novel variant in the FLCN gene in a Chinese family with Birt-Hogg-Dubé syndrome

BACKGROUND

This study aimed to identify disease-causing variants within a Chinese family affected by Birt-Hogg-Dubé syndrome (BHDS), which arises from an autosomal dominant inheritance pattern attributed to variants in the folliculin (FLCN) gene, recognized as a tumor suppressor gene.

METHODS

A Chinese proband diagnosed with BHDS due to renal tumors underwent next-generation sequencing (NGS), revealing a novel variant in the FLCN gene. Sanger sequencing was subsequently performed on blood samples obtained from family members to confirm the presence of this variant.

RESULTS

A novel germline frameshift variant (NM_144997.5:c.977dup) was identified in five individuals among the screened family members, marking the first report of this variant. Additionally, a somatic frameshift variant (NM_144997.5:c.1252del) was detected in the renal tumors of the proband. No variant was detected in unaffected family members.

CONCLUSIONS

A novel heterozygous variant was identified in exon 9 of the FLCN gene, which broadens the spectrum of FLCN variants. We recommend that molecular analysis of the FLCN gene be performed in patients with suspected BHDS and their families.

Distinct spatial landscapes in clear-cell renal cell carcinoma as revealed by whole transcriptome analysis

Background

Clear-cell renal cell carcinoma (ccRCC) is the most common and aggressive form of renal cancer and a paradigm of inter- and intratumor heterogeneity. We carried out an exploratory digital spatial profiling of the tumor interior and periphery of two ccRCC tumor specimens and mapped spatially the molecular and cellular composition of their tumor microenvironment and ecosystem.

Materials and methods

Digital spatial profiling of the whole transcriptome of 19 regions of interest (ROIs) was carried out from two selected highly immunogenic stage pT3a/grade 3 (G3) and stage pT3a/grade 4 (G4) ccRCC. A total of 9-10 ROIs were selected from distinct areas from each tumor, including tumor interior and tumor periphery, and differences in gene expression were analyzed by RNA sequencing, pathway enrichment analysis, and cell deconvolution.

Results

The distinct areas from the two locally advanced tumors displayed unique gene expression spatial patterns defining distinct biological pathways. Dimensional reduction analysis showed that the G3 ccRCC, compared to the G4 ccRCC, correlated with more variability between regions from the tumor interior and tumor periphery. Cell deconvolution analysis illustrated higher abundance of immune cells, including macrophages, myeloid dendritic cells, and CD4 T cells, and lower abundance of regulatory T cells in the tumor periphery compared to the tumor interior.

Conclusions

Transcriptome spatial profiling revealed high inter- and intratumor heterogeneity in the analyzed tumors and provided information with potential clinical utility. This included the finding of less intratumor heterogeneity and more tumor-infiltrated T cells in the ccRCC tumor specimen with a higher grade.

Hybrid Oncocytic Tumors (HOTs) in Birt-Hogg-Dubé Syndrome Patients-A Tale of Two Cities: Sequencing Analysis Reveals Dual Lineage Markers Capturing the 2 Cellular Populations of HOT

Birt-Hogg-Dubé (BHD) syndrome is associated with an increased risk of multifocal renal tumors, including hybrid oncocytic tumor (HOT) and chromophobe renal cell carcinoma (chRCC). HOT exhibits heterogenous histologic features overlapping with chRCC and benign renal oncocytoma, posing challenges in diagnosis of HOT and renal tumor entities resembling HOT. In this study, we performed integrative analysis of bulk and single-cell RNA sequencing data from renal tumors and normal kidney tissues, and nominated candidate biomarkers of HOT, L1CAM, and LINC01187 , which are also lineage-specific markers labeling the principal cell and intercalated cell lineages of the distal nephron, respectively. Our findings indicate the principal cell lineage marker L1CAM and intercalated cell lineage marker LINC01187 to be expressed mutually exclusively in a unique checkered pattern in BHD-associated HOTs, and these 2 lineage markers collectively capture the 2 distinct tumor epithelial populations seen to co-exist morphologically in HOTs. We further confirmed that the unique checkered expression pattern of L1CAM and LINC01187 distinguished HOT from chRCC, renal oncocytoma, and other major and rare renal cell carcinoma subtypes. We also characterized the histopathologic features and immunophenotypic features of oncocytosis in the background kidney of patients with BHD, as well as the intertumor and intratumor heterogeneity seen within HOT. We suggest that L1CAM and LINC01187 can serve as stand-alone diagnostic markers or as a panel for the diagnosis of HOT. These lineage markers will inform future studies on the evolution and interaction between the 2 transcriptionally distinct tumor epithelial populations in such tumors.

Comparative analyses define differences between BHD-associated renal tumour and sporadic chromophobe renal cell carcinoma

BACKGROUND

Birt-Hogg-Dubé (BHD) syndrome, caused by germline alteration of folliculin (FLCN) gene, develops hybrid oncocytic/chromophobe tumour (HOCT) and chromophobe renal cell carcinoma (ChRCC), whereas sporadic ChRCC does not harbor FLCN alteration. To date, molecular characteristics of these similar histological types of tumours have been incompletely elucidated.

METHODS

To elucidate renal tumourigenesis of BHD-associated renal tumours and sporadic renal tumours, we conducted whole genome sequencing (WGS) and RNA-sequencing (RNA-seq) of sixteen BHD-associated renal tumours from nine unrelated BHD patients, twenty-one sporadic ChRCCs and seven sporadic oncocytomas. We then compared somatic mutation profiles with FLCN variants and RNA expression profiles between BHD-associated renal tumours and sporadic renal tumours.

FINDINGS

RNA-seq analysis revealed that BHD-associated renal tumours and sporadic renal tumours have totally different expression profiles. Sporadic ChRCCs were clustered into two distinct clusters characterized by L1CAM and FOXI1 expressions, molecular markers for renal tubule subclasses. Increased mitochondrial DNA (mtDNA) copy number with fewer variants was observed in BHD-associated renal tumours compared to sporadic ChRCCs. Cell-of-origin analysis using WGS data demonstrated that BHD-associated renal tumours and sporadic ChRCCs may arise from different cells of origin and second hit FLCN alterations may occur in early third decade of life in BHD patients.

INTERPRETATION

These data further our understanding of renal tumourigenesis of these two different types of renal tumours with similar histology.

FUNDING

This study was supported by JSPS KAKENHI Grants, RIKEN internal grant, and the Intramural Research Program of the National Institutes of Health (NIH), National Cancer Institute (NCI), Center for Cancer Research.