Machine learning-based immune phenotypes correlate with STK11/KEAP1 co-mutations and prognosis in resectable NSCLC: a sub-study of the TNM-I trial

BACKGROUND

We aim to implement an immune cell score model in routine clinical practice for resected non-small-cell lung cancer (NSCLC) patients (NCT03299478). Molecular and genomic features associated with immune phenotypes in NSCLC have not been explored in detail.

PATIENTS AND METHODS

We developed a machine learning (ML)-based model to classify tumors into one of three categories: inflamed, altered, and desert, based on the spatial distribution of CD8+ T cells in two prospective (n = 453; TNM-I trial) and retrospective (n = 481) stage I-IIIA NSCLC surgical cohorts. NanoString assays and targeted gene panel sequencing were used to evaluate the association of gene expression and mutations with immune phenotypes.

RESULTS

Among the total of 934 patients, 24.4% of tumors were classified as inflamed, 51.3% as altered, and 24.3% as desert. There were significant associations between ML-derived immune phenotypes and adaptive immunity gene expression signatures. We identified a strong association of the nuclear factor-κB pathway and CD8+ T-cell exclusion through a positive enrichment in the desert phenotype. KEAP1 [odds ratio (OR) 0.27, Q = 0.02] and STK11 (OR 0.39, Q = 0.04) were significantly co-mutated in non-inflamed lung adenocarcinoma (LUAD) compared to the inflamed phenotype. In the retrospective cohort, the inflamed phenotype was an independent prognostic factor for prolonged disease-specific survival and time to recurrence (hazard ratio 0.61, P = 0.01 and 0.65, P = 0.02, respectively).

CONCLUSIONS

ML-based immune phenotyping by spatial distribution of T cells in resected NSCLC is able to identify patients at greater risk of disease recurrence after surgical resection. LUADs with concurrent KEAP1 and STK11 mutations are enriched for altered and desert immune phenotypes.

A tissue-bioengineering strategy for modeling rare human kidney diseases in vivo

The lack of animal models for some human diseases precludes our understanding of disease mechanisms and our ability to test prospective therapies in vivo. Generation of kidney organoids from Tuberous Sclerosis Complex (TSC) patient-derived-hiPSCs allows us to recapitulate a rare kidney tumor called angiomyolipoma (AML). Organoids derived from TSC2-/- hiPSCs but not from isogenic TSC2+/- or TSC2+/+ hiPSCs share a common transcriptional signature and a myomelanocytic cell phenotype with kidney AMLs, and develop epithelial cysts, replicating two major TSC-associated kidney lesions driven by genetic mechanisms that cannot be consistently recapitulated with transgenic mice. Transplantation of multiple TSC2-/- renal organoids into the kidneys of immunodeficient rats allows us to model AML in vivo for the study of tumor mechanisms, and to test the efficacy of rapamycin-loaded nanoparticles as an approach to rapidly ablate AMLs. Collectively, our experimental approaches represent an innovative and scalable tissue-bioengineering strategy for modeling rare kidney disease in vivo.

Potential location of a bladder tumor suppressor gene on chromosome 9q at 9q13 to 9q22.1

Allelic losses involving chromosome 9q occur in a significant percentage of bladder tumors. Experimental evidence suggests that a putative tumor suppressor gene located on this chromosome may play a role in the development of bladder cancer. The precise location of this potential tumor suppressor gene is not clear. Previous studies have targeted a large region between 9p12-13 and 9q22 or 9p12 and 9q34.1 as the likely site. To further delineate the location of this gene, we examined 49 tumors by loss of heterozygosity (LOH) analysis, using seven microsatellite polymorhpic loci spanning from 9p21 to 9q34 of the chromosome. LOH was found in at least one of the loci in 20 (41%) of the tumors examined, and the majority (12 of 17; 71%) of the losses on 9q involved large segments or the entire chromosome arm. Although many of the tumors with large losses on 9q also involved 9p21, several tumors with small losses did not involve the 9p marker. Conversely, there were tumors with 9p21 losses that did not involve the q-arm. These data agree with recent findings that distinct tumor suppressor genes associated with bladder cancer are located on separate arms of chromosome 9. Among tumors with single locus LOHs, the most common deletion was located in 9q 13-21.2, which was detected by probe D9S15. This also is the smallest area of critical loss when LOH patterns of tumors with partial or interstitial losses were examined. Results of the study therefore suggest that a potential tumor suppressor gene may reside within or near the region of 9q13-22.1.

Identification of driver mutations in tumor specimens from 1,000 patients with lung adenocarcinoma: The NCI’s Lung Cancer Mutation Consortium (LCMC)

CRA7506

Background: The ability to detect driver mutations like EGFR and EML4-ALK in tumor specimens from patients with lung cancer and administer agents targeting those molecular lesions has revolutionized the management of adenocarcinoma of the lung. The availability of multiplexed assays to detect mutations permits the identification of multiple driver mutations from tumors at diagnosis. The number of molecular lesions and new agents to target them continues to grow. To exploit this, we created the LCMC to determine 10 driver mutations in tumors from 1,000 patients and to give the results to clinicians for care and entry onto targeted therapeutic trials based on these findings. Methods: The 14 member LCMC is prospectively enrolling patients to test tumors from patients with lung adenocarcinoma in CLIA laboratories for KRAS, EGFR, HER2, BRAF, PIK3CA, AKT1, MEK1, and NRAS using standard multiplexed assays and fluorescence in situ hybridization (FISH) for ALK rearrangements and MET amplifications. All are stage IIIB/IV, PS 0-2, have available tissue, and signed consent. Results: 830 patients have been registered with 50 enrolling monthly. We detected a driver mutation in 60% (252/422, 95% CI 55 to 65%) of tumors thus far. Mutations found: KRAS 107 (25%, 95% CI 21 to 30%), EGFR 98 (23%, 95% CI 19 to 27%), ALK rearrangements 14 (6%, 95% CI 4 to11%), BRAF 12 (3%, 95% CI 1 to 5%), PIK3CA 11 (3%, 95% CI 1 to 5%), MET amplifications 4 (2%, 95% CI 0.5 to 5%), HER2 3, (1%, 95% CI 0.1 to 2%), MEK1 2 (0.4%, 95% CI 0.1 to 2%), NRAS 1 (0.2%, 95% CI 0.01 to 1%), AKT1 0 (0%, 95% CI 0 to 1%). 95% of molecular lesions were mutually exclusive. Conclusions: We detected an actionable driver mutation in 60% of tumors from prospectively studied patients with lung adenocarcinoma. Results of EGFR mutation testing are given to treating physicians to select erlotinib as initial treatment per NCCN and ASCO guidelines. Patients with other driver mutations are offered participation in LCMC-linked trials of agents targeting the mutation identified, e.g. crizotinib with EML4-ALK. At half of LCMC sites, multiplexed testing for all mutations is now routine practice in their pathology departments. Supported by 1RC2CA148394-01.

Distinct clinical characteristics of tuberous sclerosis complex patients with no mutation identified

Tuberous Sclerosis Complex (TSC) is a multi-system disorder that is highly variable in its clinical presentation. Current molecular diagnostic methods permit identification of mutations in either TSC1 or TSC2 in 75-85% of TSC patients. Here we examine the clinical characteristics of those TSC patients who have no mutation identified (NMI). A retrospective review of our patient population that had comprehensive testing for mutations in TSC1/TSC2 identified 23/157 (15%) that were NMI. NMI patients had a lower incidence of brain findings on imaging studies, neurological features, and renal findings than those with TSC2 mutations. In contrast, NMI patients had a lower incidence of seizures than TSC patients with TSC1 mutations, but had a higher incidence of both renal angiomyolipomas and pulmonary lymphangioleiomyomatosis. This distinct constellation of findings suggest that NMI patients may have a unique molecular pathogenesis, different from that seen in TSC patients with the usual mutations in TSC1 and TSC2. We suggest that the mechanisms of disease in these patients include both mosaicism for a TSC2 mutation, and unusual non-coding region mutations in TSC2.

Qualitative and quantitative effects of APOE genetic variation on plasma C-reactive protein, LDL-cholesterol, and apoE protein

A genetic link between lipid metabolism and inflammation has been suggested by the association between variation in the APOE gene and plasma C-reactive protein (CRP). This association was confirmed among Caucasians and extended to an African-American population, and the well-known associations of APOE variation with LDL-C and apoE protein were also observed. While eight common variants in APOE were examined, the association with CRP involved primarily the two nonsynonymous SNPs that define the major epsilon2, epsilon3, and epsilon4 alleles. In particular, the strongest link involved lower CRP levels among carriers of the APOE epsilon4 allele that also contributes to the risk of cardiovascular and Alzheimer's diseases as well as to higher lipid levels. A lesser effect was characterized by lower CRP levels among carriers of a subtype of the epsilon3 allele. The magnitude of the association with plasma CRP was at least as great as the effect of variation in the CRP gene itself. Quantitative analysis suggested that the effect on CRP is more likely a consequence of intrinsic functional differences among the E2, E3, and E4 apoE proteins than different levels of apoE protein or LDL-C in the plasma.

Qualitative and quantitative effects of APOE genetic variation on plasma C-reactive protein, LDL-cholesterol, and apoE protein

A genetic link between lipid metabolism and inflammation has been suggested by the association between variation in the APOE gene and plasma C-reactive protein (CRP). This association was confirmed among Caucasians and extended to an African-American population, and the well-known associations of APOE variation with LDL-C and apoE protein were also observed. While eight common variants in APOE were examined, the association with CRP involved primarily the two nonsynonymous SNPs that define the major epsilon2, epsilon3, and epsilon4 alleles. In particular, the strongest link involved lower CRP levels among carriers of the APOE epsilon4 allele that also contributes to the risk of cardiovascular and Alzheimer's diseases as well as to higher lipid levels. A lesser effect was characterized by lower CRP levels among carriers of a subtype of the epsilon3 allele. The magnitude of the association with plasma CRP was at least as great as the effect of variation in the CRP gene itself. Quantitative analysis suggested that the effect on CRP is more likely a consequence of intrinsic functional differences among the E2, E3, and E4 apoE proteins than different levels of apoE protein or LDL-C in the plasma.

Influence of genetic variation in the C-reactive protein gene on the inflammatory response during and after acute coronary ischemia

The aim of this research was to assess whether common genetic variants within the C-reactive protein gene (CRP) are related to the degree of acute rise in plasma C-reactive protein (CRP) levels following an acute coronary syndrome (ACS). While polymorphisms within CRP are associated with basal CRP levels in healthy men and women, less is known about the relationship of such genetic variants and the degree of CRP rise during and after acute ischemia. Plasma CRP is associated with increased rates of recurrent coronary events. We evaluated seven common genetic variants within CRP and assessed their relationship to the degree of rise in CRP levels immediately following an acute coronary syndrome in 1827 European American patients. Variants in the putative promoter region, -757T > C and -286C > T > A, were associated with the highest CRP elevations after ACS. Patients with two copies of the A allele of SNP -286C > T > A had median CRP values of 76.6 mg/L, compared to 11.1 mg/L in patients with no copies of the rare variant (p-value <0.0001), post ACS. The lowest CRP values were found for patients with minor alleles of the exonic 1059G > C and the 3'untranslated region 1846G > A SNPs. For example, patients homozygous for the minor allele of 1059G > C had 71% lower median CRP values than those homozygous for the major allele [3.5 vs 12.0 mg/L, p < 0.0001]. These trends persisted in the chronic stable phase after ischemia had resolved, and after adjustment for infarct size by peak creatinine kinase levels and clinical status by Killip class. Assessment of CRP genetic variants identified patients with higher and lower CRP elevation after acute coronary syndrome.

Genetic determinants of C-reactive protein in COPD

Chronic obstructive pulmonary disease (COPD) is associated with a systemic inflammatory state, marked by elevations in serum inflammatory markers including C-reactive protein (CRP). The present study sought to determine epidemiological predictors of CRP levels, to estimate the genetic influence on CRP levels, and to identify genetic variants that affect CRP in a family-based study of COPD. CRP was measured by a high-sensitivity assay in participants from the Boston Early-Onset COPD Study. Predictors of CRP level were determined using multilevel linear models. Variance component analysis was used to estimate heritability and to perform genome-wide linkage analysis for CRP levels. Two variants in the surfactant protein B (SFTPB) gene were tested for association with CRP levels. Increased age, female sex, higher body mass index, greater smoking pack-yrs and reduced forced expiratory volume in one second were all associated with increased CRP levels. There was a significant genetic influence on CRP (heritability = 0.25). Genome-wide linkage analysis revealed several potentially interesting chromosomal regions, though no significant evidence for linkage was found. A short tandem repeat marker near SFTPB was significantly associated with CRP levels. There is a genetic influence on C-reactive protein levels in chronic obstructive pulmonary disease patients. Preliminary evidence suggests an association of the surfactant protein B gene with systemic inflammation in chronic obstructive pulmonary disease.

Association of CommonCRPGene Variants with CRP Levels and Cardiovascular Events

C-reactive protein (CRP) is a well-documented marker of atherosclerotic cardiovascular disease risk. We resequenced CRP to identify a comprehensive set of common SNP variants, then studied and replicated their association with baseline CRP level among apparently healthy subjects in the Women's Health Study (WHS; n = 717), Pravastatin Inflammation/CRP Evaluation trial (PRINCE; n = 1,110) and Physicians' Health Study (PHS; n = 509) cohorts. The minor alleles of four SNPs were consistently associated in all three cohorts with higher CRP, while the minor alleles of two SNPs were associated with lower CRP (p < 0.05 for each). Single marker and haplotype analysis in all three cohorts were consistent with functional roles for the 5'-flanking triallelic SNP -286C>T>A and the 3'-UTR SNP 1846G>A. None of the SNPs associated with higher CRP were associated with risk of incident myocardial infarction (MI) or ischemic stroke in a prospective, nested case-control study design from the PHS cohort (610 case-control pairs). One SNP, -717A>G, was unrelated to CRP levels but associated with decreased risk of MI (p = 0.001). Taken together, these data imply significant interactions between both genetic and environmental contributions to the increased CRP levels that predict a greater risk of future atherothrombotic events in epidemiological studies.

Toll-like receptor 6 gene (TLR6): single-nucleotide polymorphism frequencies and preliminary association with the diagnosis of asthma

Toll-like receptor 6 (TLR6) is one of a series of highly conserved innate immune receptors. We resequenced TLR6 in DNA samples from 24 African Americans, 23 European Americans, and 24 Hispanic Americans, identifying 53 SNPs, 22 with an allele frequency >5%. Significant differences in SNP frequencies among the three populations were noted. In all, 11 SNPs caused amino-acid changes, including one with a frequency >5% in all three populations. Utilizing this SNP (Ser249Pro), we performed exploratory nested case-control disease-association studies, including one involving 56 African Americans with asthma and 93 African American controls. The minor allele of this SNP was associated with decreased risk for asthma (odds ratio 0.38, 95% CI 0.16-0.87, P=0.01), an effect consistent with the known biology of the toll-like receptors. Although replication of this finding in other, larger samples is needed, variation in TLR6 may have relevance to the pathogenesis of immunologically mediated diseases.

A family with seizures and minor features of tuberous sclerosis and a novel TSC2 mutation

The authors studied nine members of a family that demonstrated a limited form of tuberous sclerosis complex (TSC). Cutaneous findings were limited to hypopigmented macules in four patients. Five family members had recurrent seizures, and three of these had migrational defects of the cerebral mantle. Mutational analysis of TSC2 indicated the presence of the novel missense change 3106T-->C, 1036S-->P in all family members with seizures. The findings suggest that this mild variant form of TSC is due to a novel TSC2 mutation.

Tuberous sclerosis: from tubers to mTOR

Tuberous sclerosis (TSC) is an autosomal dominant hamartoma syndrome whose causative genes (TSC1 and TSC2) were identified 5 and 9 years ago respectively. Their encoded proteins are large, and apart from a strong binding interaction with each other, relatively little was known about their biochemical function. Recent studies in Drosophila have pinpointed a critical function for the DrosophilaTSC1/TSC2 homologues in the regulation of cell size. Epistasis experiments and a variety of biochemical studies that followed have indicated a critical function for these proteins in the highly conserved PI-3-kinase-Akt-mTOR signalling pathway.

Comparisons of CapG and gelsolin-null macrophages: demonstration of a unique role for CapG in receptor-mediated ruffling, phagocytosis, and vesicle rocketing

Capping the barbed ends of actin filaments is a critical step for regulating actin-based motility in nonmuscle cells. The in vivo function of CapG, a calcium-sensitive barbed end capping protein and member of the gelsolin/villin family, has been assessed using a null Capg allele engineered into mice. Both CapG-null mice and CapG/gelsolin double-null mice appear normal and have no gross functional abnormalities. However, the loss of CapG in bone marrow macrophages profoundly inhibits macrophage colony stimulating factor-stimulated ruffling; reintroduction of CapG protein by microinjection fully restores this function. CapG-null macrophages also demonstrate approximately 50% impairment of immunoglobulin G, and complement-opsonized phagocytosis and lanthanum-induced vesicle rocketing. These motile functions are not impaired in gelsolin-null macrophages and no additive effects are observed in CapG/gelsolin double-null macrophages, establishing that CapG function is distinct from, and does not overlap with, gelsolin in macrophages. Our observations indicate that CapG is required for receptor-mediated ruffling, and that it is a major functional component of macrophage phagocytosis. These primary effects on macrophage motile function suggest that CapG may be a useful target for the regulation of macrophage-mediated inflammatory responses.

Mutational and radiographic analysis of pulmonary disease consistent with lymphangioleiomyomatosis and micronodular pneumocyte hyperplasia in women with tuberous sclerosis

Lymphangioleiomyomatosis (LAM) and multifocal micronodular pneumocyte hyperplasia (MMPH) produce cystic and nodular disease, respectively, in the lungs of patients with tuberous sclerosis. The objective of this study was to prospectively characterize the prevalence, clinical presentation, and genetic basis of lung disease in TSC. We performed genotyping and computerized tomographic (CT) scanning of the chest on 23 asymptomatic women with tuberous sclerosis complex (TSC). Cystic pulmonary parenchymal changes consistent with LAM were found in nine patients (39%). These patients tended to be older than cyst-negative patients (31.9 +/- 7.6 yr versus 24.8 +/- 11.6 yr, p = 0.09). There was no correlation between presence of cysts and tobacco use, age at menarche, history of pregnancy, or estrogen-containing medications. Three of the cyst-positive patients had a prior history of pneumothorax. Pulmonary function studies revealed evidence of gas trapping but normal spirometric indices in the cyst-positive group. All nine cyst-positive patients had angiomyolipomas (AML), which were larger (p < 0.05) and more frequently required intervention (p = 0.08) than cyst-negative patients (8 of 14 with AMLs, p < 0.05). Ten patients (43%) had pulmonary parenchymal nodules. Pulmonary nodules were more common in women with cysts (78% versus 21%, p < 0.05), and 52% of all patients had either cystic or nodular changes. TSC2 mutations were identified in all cyst-positive patients who were tested (n = 8), whereas both TSC1 and TSC2 mutations were found in patients with nodular disease. Correlation of the mutational and radiographic data revealed one pair of sisters who were discordant for cystic disease, two mother- daughter pairs who were discordant for nodular disease, and no clear association between cyst development and a specific mutational type. This prospective analysis demonstrates that cystic and nodular pulmonary changes consistent with LAM and MMPH are common in women with TSC.

Gelsolin as a negative prognostic factor and effector of motility in erbB-2-positive epidermal growth factor receptor-positive breast cancers

PURPOSE

erbB-2 and epidermal growth factor receptor (EGFR) may mediate motility via signaling that enables changes in the actin cytoskeleton. A physical basis for this motility may depend on the coexpression of gelsolin, a M(r) 80,000 actin-binding protein.

EXPERIMENTAL DESIGN

The expression of erbB-2, EGFR, and gelsolin was analyzed in 790 archival invasive breast cancers. These data were compared with histological, clinical, and outcome data (median follow-up, 16.3 years).

RESULTS

Protein overexpression was observed in overlapping subsets of breast cancers (38% of cases were erbB-2+; 15% of cases were EGFR+; and 56% of cases were gelsolin+). Tumor gelsolin was associated with overexpression of erbB-2 and EGFR, as well as with an aggressive tumor phenotype. By univariate and multivariate analyses, tumor gelsolin alone was not a prognostic factor. Overexpression of all three factors significantly predicted poor clinical outcome by univariate and multivariate analyses. For example, in node-positive patients, coexpression of all three markers was associated with a 3-year disease-specific survival (as compared with erbB-2+, EGFR+, gelsolin- patients, who had a median survival of 6 years).

CONCLUSIONS

These data suggest that gelsolin coexpression may be an important additional prognostic factor in erbB-2+, EGFR+ breast cancer patients. We hypothesize that this is due to the role of gelsolin in mediating motility and invasion.

Profilin I is essential for cell survival and cell division in early mouse development

Profilins are thought to play a central role in the regulation of de novo actin assembly by preventing spontaneous actin polymerization through the binding of actin monomers, and the adding of monomeric actin to the barbed actin-filament ends. Other cellular functions of profilin in membrane trafficking and lipid based signaling are also likely. Binding of profilins to signaling molecules such as Arp2/3 complex, Mena, VASP, N-WASP, dynamin I, and others, further implicates profilin and actin as regulators of diverse motile activities. In mouse, two profilins are expressed from two distinct genes. Profilin I is expressed at high levels in all tissues and throughout development, whereas profilin II is expressed in neuronal cells. To examine the function of profilin I in vivo, we generated a null profilin I (pfn1(ko)) allele in mice. Homozygous pfn1(ko/ko) mice are not viable. Pfn1(ko/ko) embryos died as early as the two-cell stage, and no pfn1(ko/ko) blastocysts were detectable. Adult pfn1(ko/wt) mice show a 50% reduction in profilin I expression with no apparent impairment of cell function. However, pfn1(ko/wt) embryos have reduced survival during embryogenesis compared with wild type. Although weakly expressed in early embryos, profilin II cannot compensate for lack of profilin I. Our results indicate that mouse profilin I is an essential protein that has dosage-dependent effects on cell division and survival during embryogenesis.

Denaturing high-performance liquid chromatography (DHPLC) is a highly sensitive, semi-automated method for identifying mutations in the TSC1 gene

Sensitive and automated methods for the detection of DNA sequence variation are required for a wide variety of genetic studies. Diagnostic testing in human genetic disorders is one application of such methods. Tuberous sclerosis complex (TSC) is an autosomal dominant familial tumor syndrome characterized by the development of benign tumors (hamartomas) in multiple organs (OMIM # 19110, #191092). There is a high frequency of sporadic cases and significant demand from patients and families for genetic testing information. Two TSC genes have been identified (TSC1 and TSC2) and together account for all cases [1,2]. Here we report our methods for DHPLC analysis of the TSC1 gene and demonstrate the high sensitivity of this method in a blinded analysis of 21 TSC patients with known TSC1 mutations. In this series, DHPLC detected 27/28 (96%) known TSC1 sequence variations. The only sequence variation not identified by DHPLC in this study is a mosaic case.

Bronchioloalveolar carcinoma of the lung: recurrences and survival in patients with stage I disease

OBJECTIVES

The aim of our study was to retrospectively compare the patient characteristics, the frequency and pattern of recurrent disease, and survival in patients with stage I bronchioloalveolar carcinoma and adenocarcinoma of the lung.

METHODS

Patients with stage I bronchioloalveolar carcinoma or adenocarcinoma other than bronchioloalveolar carcinoma resected between 1984 and 1992 with adequate clinical follow-up were studied. The clinical characteristics of the patients, extent of initial surgical resection, sites of recurrent disease, and overall survival were examined and compared between the 2 groups. The median follow-up for patients with bronchioloalveolar carcinoma and adenocarcinoma was 6.2 years and 5.9 years, respectively.

RESULTS

A total of 138 patients were identified. Thirty-three patients had bronchioloalveolar carcinoma and 105 patients had adenocarcinoma. Eleven (33%) of the patients with bronchioloalveolar carcinoma had never smoked cigarettes versus 9 (9%) of the patients with adenocarcinoma (P =.0036). There were no significant differences between patients with bronchioloalveolar carcinoma and adenocarcinoma in sex distribution and overall recurrence rate. Of the 12 patients with recurrent bronchioloalveolar carcinoma, 1 patient (8%) had extrathoracic disease develop at the site of first recurrence compared with 49% of patients with recurrent adenocarcinoma (P <.001). The 5-year survival in patients with bronchioloalveolar carcinoma and in those with adenocarcinoma was 83% and 63%, respectively (P =.04).

CONCLUSIONS

Stage I bronchioloalveolar carcinoma is more likely to occur in nonsmokers. Survival is longer in patients with bronchioloalveolar carcinoma. Further research is warranted to define the etiology, clinical course, and molecular abnormalities in patients with bronchioloalveolar carcinoma to generate more effective therapeutic approaches.

The mouse mammary gland requires the actin-binding protein gelsolin for proper ductal morphogenesis

Gelsolin is an actin-binding/severing protein expressed in intracellular and secreted forms. It is a major regulator of the form and function of the actin cytoskeleton in most all cells. Here we demonstrate that female mice with a targeted deletion of the gelsolin gene (Gsn-/-) have defects in mammary gland morphogenesis. Two distinct defects were identified in the gelsolin-null mammary gland. First, the mammary anlage from Gsn-/- mice failed to elongate at the onset of puberty and remained rudimentary until approximately 9 weeks of age, early block (Gsn-/-(EB)). Second, after the mammary epithelium had filled the mammary fat pad, a complete lack of terminal branching, or late block, was observed (Gsn-/-(LB)). The Gsn-/-(EB) was seen in 70% of Gsn-/- mice and appeared to be dependent on a modifier gene(s) in addition to the loss of gelsolin. Gsn-/-(LB) was observed in all Gsn-/- mice. Terminal end buds (TEBs) were not evident in the mammary anlage from Gsn-/-(EB) mice until approximately 9 weeks of age. Cellular proliferation in the terminal ductal regions of Gsn-/-(EB) females was detected by bromodeoxyuridine incorporation, but was less than that found in the TEBs of age-matched controls. In mice deficient for gelsolin, mammary gland architecture was unaltered at the histological level. Lobuloalveolar development was delayed in response to pregnancy in mammary glands of Gsn-/- mice but was otherwise normal. Lactation and involution in the gelsolin-null animals were similar to those of wild-type mice. Transplantation of epithelium devoid of gelsolin into a wild-type (GsnWT) mammary fat pad resulted in proper arborization of the ductal tree. Transplantation of GsnWT epithelium into the Gsn-/- fat pad recapitulated the lack of terminal branching seen in Gsn-/- females. These results indicate that gelsolin is required in the mammary stroma for proper ductal morphogenesis. Our results provide the first evidence of an actin regulatory protein affecting mammary ductal growth through stromal-epithelial communication.