Differences in polygenic score distributions in European ancestry populations: implications for breast cancer risk prediction

The 313-variant polygenic risk score (PRS313) provides a promising tool for breast cancer risk prediction. However, evaluation of the PRS313 across different European populations which could influence risk estimation has not been performed. Here, we explored the distribution of PRS313 across European populations using genotype data from 94,072 females without breast cancer, of European-ancestry from 21 countries participating in the Breast Cancer Association Consortium (BCAC) and 225,105 female participants from the UK Biobank. The mean PRS313 differed markedly across European countries, being highest in south-eastern Europe and lowest in north-western Europe. Using the overall European PRS313 distribution to categorise individuals leads to overestimation and underestimation of risk in some individuals from south-eastern and north-western countries, respectively. Adjustment for principal components explained most of the observed heterogeneity in mean PRS. Country-specific PRS distributions may be used to calibrate risk categories in individuals from different countries.

Genome-wide association study of treatment-related toxicity two years following radiotherapy for breast cancer

BACKGROUND AND PURPOSE

Up to a quarter of breast cancer patients treated by surgery and radiotherapy experience clinically significant toxicity. If patients at high risk of adverse effects could be identified at diagnosis, their treatment could be tailored accordingly. This study was designed to identify common single nucleotide polymorphisms (SNPs) associated with toxicity two years following whole breast radiotherapy.

MATERIALS AND METHODS

A genome-wide association study (GWAS) was performed in 1,640 breast cancer patients with complete SNP, clinical, treatment and toxicity data, recruited across 18 European and US centres into the prospective REQUITE cohort study. Toxicity data (CTCAE v4.0) were collected at baseline, end of radiotherapy, and annual follow-up. A total of 7,097,340 SNPs were tested for association with the residuals of toxicity endpoints, adjusted for clinical, treatment co-variates and population substructure.

RESULTS

Quantile-quantile plots showed more associations with toxicity above the p < 5 × 10-5 level than expected by chance. Eight SNPs reached genome-wide significance. Nipple retraction grade ≥ 2 was associated with the rs188287402 variant (p = 2.80 × 10-8), breast oedema grade ≥ 2 with rs12657177 (p = 1.12 × 10-10), rs75912034 (p = 1.12 × 10-10), rs145328458 (p = 1.06 × 10-9) and rs61966612 (p = 1.23 × 10-9), induration grade ≥ 2 with rs77311050 (p = 2.54 × 10-8) and rs34063419 (p = 1.21 × 10-8), and arm lymphoedema grade ≥ 1 with rs643644 (p = 3.54 × 10-8). Heritability estimates across significant endpoints ranged from 25% to 39%. Our study did not replicate previously reported SNPs associated with breast radiation toxicity at the pre-specified significance level.

CONCLUSIONS

This GWAS for long-term breast radiation toxicity provides further evidence for significant association of common SNPs with distinct toxicity endpoints.

Abstract P1-02-04: Real world adjuvant endocrine treatment in premenopausal breast cancer patients compared with the proposed algorithm using the Regan Composite Risk Score

Background The Regan Composite Risk Score (RCRS) is a web-based prognostic and predictive calculator to guide the use of adjuvant exemestane plus ovarian function suppression (AI + OFS) versus tamoxifen plus ovarian function suppression (TAM + OFS) or tamoxifen alone (TAM) for premenopausal women with hormone receptor-positive HER2-negative early breast cancer (HR+/HER2- EBC). We compared our adjuvant endocrine therapy policy based on the tumor board with the treatment guided by the RCRS during 2 time periods, one before and one after the acquaintance of the Tamoxifen and Exemestane Trial (TEXT) and Suppression and Ovarian Function Trial (SOFT) data. This allowed us to see a possible evolution in therapy policy. Methods A retrospective cohort study of 563 premenopausal patients with HR+/HER2- and HER2+ EBC diagnosed at the University Hospital of Leuven during 2 periods, 2010-2012 (cohort 1) and 2015-2017 (cohort 2), was conducted. For each patient with HER2- EBC, the RCRS was calculated by entering the requested characteristics in the online available tool. The primary outcome was to investigate how frequent our therapy differed from the therapy guided by the RCRS based on the estimated 8-yr distant relapse free interval (DRFI) with an arbitrary cut-off set at 3 %. If the received therapy was ≥ 3 % less efficient in 8-year DRFI compared to the optimal therapy according to RCRS, the patient was considered undertreated. If the received therapy differed by less than 3 % in 8-year DRFI compared to the optimal therapy according to RCRS and yet the most intensive therapy (AI + OFS &gt; TAM + OFS &gt; TAM) was administered, the patient was considered overtreated. In the other cases, the patient was considered to have been treated concordant with the RCRS. Secondarily, nonadherence of the HER2- and HER2+ patients towards the endocrine treatments leading to therapy switch because of intolerance was recorded at 6, 12, 24 and 36 months. Analyses were performed using SAS software and the comparison of both cohorts was performed by the chi-squared test for categorical variables. Results According to the RCRS, 43.2 % (89/206) of the HER2-negative patients of cohort 1 were undertreated compared to 22.1 % (43/194) in cohort 2 (chi- squared test, p-value &lt; 0.001). The number of overtreated patients also differed significantly between the two cohorts (chi-squared test, p-value = 0.003) with 2.9 % (6/206) in the first cohort and 10.3 % (20/194) in the second cohort. Finally, the number of patients treated concordant with the guidance derived from the RCRS was 53.9 % (111/206) in cohort 1 and 67.5 % (131/194) in cohort 2 (chi-squared test, p-value = 0.005). Treatment intolerance and switch was observed in 34.8 %, 16.7 % and 12.4 % of the patients receiving AI + OFS, TAM + OFS or TAM as initial therapy respectively; this was numerically higher for all treatments in cohort 2 vs cohort 1, although the observed difference was only significant for TAM. Conclusion In our center, a recent cohort of premenopausal women was more likely to be treated with the adjuvant endocrine treatment concordant with the guidance derived from the RCRS when using an arbitrary cut-off of 3 % to define a relevant improvement in outcome.

Citation Format: Charlotte Berteloot, Patrick Neven, Maja Vangoitsenhoven, Annouschka Laenen, Hans Wildiers, Kevin Punie, Ann Smeets, Ines Nevelsteen, Sileny Han, Thaïs Baert, Hilde Janssen, Eva Oldenburger, Adinda Baten, Patrick Berteloot, Rani Vanhoudt, Anne Deblander, Chantal Remmeriev, Christine Desmedt. Real world adjuvant endocrine treatment in premenopausal breast cancer patients compared with the proposed algorithm using the Regan Composite Risk Score [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-02-04.

Common variants in breast cancer risk loci predispose to distinct tumor subtypes

BACKGROUND

Genome-wide association studies (GWAS) have identified multiple common breast cancer susceptibility variants. Many of these variants have differential associations by estrogen receptor (ER) status, but how these variants relate with other tumor features and intrinsic molecular subtypes is unclear.

METHODS

Among 106,571 invasive breast cancer cases and 95,762 controls of European ancestry with data on 173 breast cancer variants identified in previous GWAS, we used novel two-stage polytomous logistic regression models to evaluate variants in relation to multiple tumor features (ER, progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2) and grade) adjusting for each other, and to intrinsic-like subtypes.

RESULTS

Eighty-five of 173 variants were associated with at least one tumor feature (false discovery rate < 5%), most commonly ER and grade, followed by PR and HER2. Models for intrinsic-like subtypes found nearly all of these variants (83 of 85) associated at p < 0.05 with risk for at least one luminal-like subtype, and approximately half (41 of 85) of the variants were associated with risk of at least one non-luminal subtype, including 32 variants associated with triple-negative (TN) disease. Ten variants were associated with risk of all subtypes in different magnitude. Five variants were associated with risk of luminal A-like and TN subtypes in opposite directions.

CONCLUSION

This report demonstrates a high level of complexity in the etiology heterogeneity of breast cancer susceptibility variants and can inform investigations of subtype-specific risk prediction.

Mendelian randomisation study of smoking exposure in relation to breast cancer risk

BACKGROUND

Despite a modest association between tobacco smoking and breast cancer risk reported by recent epidemiological studies, it is still equivocal whether smoking is causally related to breast cancer risk.

METHODS

We applied Mendelian randomisation (MR) to evaluate a potential causal effect of cigarette smoking on breast cancer risk. Both individual-level data as well as summary statistics for 164 single-nucleotide polymorphisms (SNPs) reported in genome-wide association studies of lifetime smoking index (LSI) or cigarette per day (CPD) were used to obtain MR effect estimates. Data from 108,420 invasive breast cancer cases and 87,681 controls were used for the LSI analysis and for the CPD analysis conducted among ever-smokers from 26,147 cancer cases and 26,072 controls. Sensitivity analyses were conducted to address pleiotropy.

RESULTS

Genetically predicted LSI was associated with increased breast cancer risk (OR 1.18 per SD, 95% CI: 1.07-1.30, P = 0.11 × 10-2), but there was no evidence of association for genetically predicted CPD (OR 1.02, 95% CI: 0.78-1.19, P = 0.85). The sensitivity analyses yielded similar results and showed no strong evidence of pleiotropic effect.

CONCLUSION

Our MR study provides supportive evidence for a potential causal association with breast cancer risk for lifetime smoking exposure but not cigarettes per day among smokers.

Gene-Environment Interactions Relevant to Estrogen and Risk of Breast Cancer: Can Gene-Environment Interactions Be Detected Only among Candidate SNPs from Genome-Wide Association Studies?

In this study we aim to examine gene-environment interactions (GxEs) between genes involved with estrogen metabolism and environmental factors related to estrogen exposure. GxE analyses were conducted with 1970 Korean breast cancer cases and 2052 controls in the case-control study, the Seoul Breast Cancer Study (SEBCS). A total of 11,555 SNPs from the 137 candidate genes were included in the GxE analyses with eight established environmental factors. A replication test was conducted by using an independent population from the Breast Cancer Association Consortium (BCAC), with 62,485 Europeans and 9047 Asians. The GxE tests were performed by using two-step methods in GxEScan software. Two interactions were found in the SEBCS. The first interaction was shown between rs13035764 of NCOA1 and age at menarche in the GE|2df model (p-2df = 1.2 × 10-3). The age at menarche before 14 years old was associated with the high risk of breast cancer, and the risk was higher when subjects had homozygous minor allele G. The second GxE was shown between rs851998 near ESR1 and height in the GE|2df model (p-2df = 1.1 × 10-4). Height taller than 160 cm was associated with a high risk of breast cancer, and the risk increased when the minor allele was added. The findings were not replicated in the BCAC. These results would suggest specificity in Koreans for breast cancer risk.

The microbiome of diabetic foot ulcers: a comparison of swab and tissue biopsy wound sampling techniques using 16S rRNA gene sequencing

Background

Health-care professionals need to collect wound samples to identify potential pathogens that contribute to wound infection. Obtaining appropriate samples from diabetic foot ulcers (DFUs) where there is a suspicion of infection is of high importance. Paired swabs and tissue biopsies were collected from DFUs and both sampling techniques were compared using 16S rRNA gene sequencing.

Results

Mean bacterial abundance determined using quantitative polymerase chain reaction (qPCR) was significantly lower in tissue biopsies (p = 0.03). The mean number of reads across all samples was significantly higher in wound swabs \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \Big(\overline{X} $$\end{document}(X¯ = 32,014) compared to tissue (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \overline{X} $$\end{document}X¯ = 15,256, p = 0.001). Tissue biopsies exhibited greater overall diversity of bacteria relative to swabs (Shannon’s H diversity p = 0.009). However, based on a presence/absence analysis of all paired samples, the frequency of occurrence of bacteria from genera of known and potential pathogens was generally higher in wound swabs than tissue biopsies. Multivariate analysis identified significantly different bacterial communities in swabs compared to tissue (p = 0.001). There was minimal correlation between paired wound swabs and tissue biopsies in the number and types of microorganisms. RELATE analysis revealed low concordance between paired DFU swab and tissue biopsy samples (Rho = 0.043, p = 0.34).

Conclusions

Using 16S rRNA gene sequencing this study identifies the potential for using less invasive swabs to recover high relative abundances of known and potential pathogen genera from DFUs when compared to the gold standard collection method of tissue biopsy.

Abstract P3-08-31: Clinical and pathological features of invasive micropapillary carcinoma of the breast and correlation with prognosis

Background and objective: Invasive micropapillary carcinoma (IMPC) of the breast is a special variant of breast carcinoma with a unique morphology. Data about long-term outcome are conflicting and reports on stromal tumor infiltrating lymphocytes (sTILs) and their correlation with prognosis are scarce. In this retrospective cohort study we aimed to describe clinical and pathological features of IMPC, including sTILs assessment and immunohistochemistry studies, and their correlation with long-term outcome. Materials and methods: Patients with stage I-III IMPC (pure and mixed forms) who underwent upfront surgery at our institution between 2000 and 2016 were included. All patients signed informed consent. Standard clinico-pathological features and follow-up data to calculate distant relapse-free interval and breast cancer-specific survival were obtained from clinical records. Pathologic review of representative H&E-slides of the resection specimens included evaluation of sTILs and assessment of the micropapillary component. Surrogate molecular subtypes were based on receptor-status and histological grade. Using tissue microarrays we assessed by immunohistochemistry the pattern of staining of P53, and scored semi-qualitatively the expression of Bcl2, PAX8 and WT1. The association between predictors and outcome is analyzed using the Fine and Gray model, accounting for other-cause death as competing event. All tests are two-sided, assuming a 5% significance level. The sample size did not allow multivariate analysis. Results: We included 111 patients (median age 61,5 years; range 33-88). Luminal surrogate subtypes were most prevalent with 51 luminal A-like, 41 luminal B-like, 12 luminal HER2+, 5 HER2+ and 2 triple negative IMPC. 89% of patients had a T1 or T2 tumor and 50% of IMPC were poorly differentiated. Lymph node involvement was present in 59% and lymphovascular invasion in 44% of cases. Adjuvant chemotherapy, radiotherapy and endocrine therapy was administered in 47%, 87% and 90% of patients, respectively. Of all cases 59% were pure IMPC. Standard clinico-pathological features were comparable between pure and non-pure IMPC. sTILs were classified as low (&lt;30%), intermediate (30-50%) and high (&gt;50%) in 78%, 14% and 8% of specimens respectively. Comparison between surrogate subtypes showed higher sTILs (p=0.025) and a higher likelihood of aberrant P53 expression (p&lt;0.001) in HER2+ compared to luminal A-like subtype. Immunohistochemistry studies performed on 105 samples with enough material showed aberrant P53 expression in 10% and WT1 nuclear expression in 7% of cases. Pax8-staining was negative in all IMPC in this cohort. Bcl-2 expression was strongly related to all luminal subtypes (p&lt;0.03). After a median follow-up of 100 months, we observed 8 distant relapses (7,2%) and 3 breast cancer-related deaths (2,7%). All events occurred in non-pure IMPC. Surrogate subtypes for patients with distant relapses where luminal A-like in 4 patients while the other subtypes where each observed in 1 patient. Five out of eight patients with distant relapse had received prior adjuvant chemotherapy. Six had lymph node involvement. Higher median sTILs was correlated with worse distant relapse-free interval (HR=1.55; p=0.0172) and breast cancer-specific survival (HR=2.10; p&lt;0.001). Conclusions: Standard clinico-pathological features were similar in pure and non-pure IMPC. Despite high proportion of grade 3 differentiation and lymph node involvement, we observed a low rate of distant metastasis and within the pure IMPC (59% of patients), no distant relapses occurred. These findings could be explained by the high proportion of luminal-A like tumors in our cohort and need confirmation. Higher sTILs was associated with worse outcome in this IMPC cohort, confirming previously published observations.

Citation Format: Kevin Punie, Frederik Deman, Annouschka Laenen, Timothy Faes, Hans Wildiers, Ann Smeets, Ines Nevelsteen, Chantal Van Ongeval, Adinda Baten, Melissa Christiaens, Eva Oldenburger, Hilde Janssen, Caroline Weltens, Tatjana Geukens, Nynke Willers, Jan Ardui, Hava Izci, Laurence Slembrouck, Patrick Neven, Christine Desmedt, Giuseppe Floris. Clinical and pathological features of invasive micropapillary carcinoma of the breast and correlation with prognosis [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-08-31.

Comparative genomics of Eucalyptus and Corymbia reveals low rates of genome structural rearrangement

BACKGROUND

Previous studies suggest genome structure is largely conserved between Eucalyptus species. However, it is unknown if this conservation extends to more divergent eucalypt taxa. We performed comparative genomics between the eucalypt genera Eucalyptus and Corymbia. Our results will facilitate transfer of genomic information between these important taxa and provide further insights into the rate of structural change in tree genomes.

RESULTS

We constructed three high density linkage maps for two Corymbia species (Corymbia citriodora subsp. variegata and Corymbia torelliana) which were used to compare genome structure between both species and Eucalyptus grandis. Genome structure was highly conserved between the Corymbia species. However, the comparison of Corymbia and E. grandis suggests large (from 1-13 MB) intra-chromosomal rearrangements have occurred on seven of the 11 chromosomes. Most rearrangements were supported through comparisons of the three independent Corymbia maps to the E. grandis genome sequence, and to other independently constructed Eucalyptus linkage maps.

CONCLUSIONS

These are the first large scale chromosomal rearrangements discovered between eucalypts. Nonetheless, in the general context of plants, the genomic structure of the two genera was remarkably conserved; adding to a growing body of evidence that conservation of genome structure is common amongst woody angiosperms.

Inducing pluripotency in vitro: recent advances and highlights in induced pluripotent stem cells generation and pluripotency reprogramming

Induced pluripotent stem cells (iPSCs) are considered patient-specific counterparts of embryonic stem cells as they originate from somatic cells after forced expression of pluripotency reprogramming factors Oct4, Sox2, Klf4 and c-Myc. iPSCs offer unprecedented opportunity for personalized cell therapies in regenerative medicine. In recent years, iPSC technology has undergone substantial improvement to overcome slow and inefficient reprogramming protocols, and to ensure clinical-grade iPSCs and their functional derivatives. Recent developments in iPSC technology include better reprogramming methods employing novel delivery systems such as non-integrating viral and non-viral vectors, and characterization of alternative reprogramming factors. Concurrently, small chemical molecules (inhibitors of specific signalling or epigenetic regulators) have become crucial to iPSC reprogramming; they have the ability to replace putative reprogramming factors and boost reprogramming processes. Moreover, common dietary supplements, such as vitamin C and antioxidants, when introduced into reprogramming media, have been found to improve genomic and epigenomic profiles of iPSCs. In this article, we review the most recent advances in the iPSC field and potent application of iPSCs, in terms of cell therapy and tissue engineering.

Imaging findings of a cutaneous B-cell lymphoma

We report a case of a slowly growing primary cutaneous B-cell lymphoma of the right upper arm in an 81-old-year-old female. Although primary cutaneous lymphoma is the second most common group of extranodal non-Hodgkin lymphomas, reports on the potential value of imaging in the diagnosis are very scarce in the radiological literature. Although the dermatologist usually relies on clinical and histological findings for a correct diagnosis, MR imaging may be useful in local staging of the tumor, whereas 18F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) is the imaging technique of choice for initial distant staging and follow-up after treatment.

Effects of inositol hexaphosphate on growth and differentiation in K-562 erythroleukemia cell line

Inositol hexaphosphate (InsP6) has recently been shown to inhibit experimental cancers in vivo. Since the lower phosphorylated forms of InsP6 are important in cell growth in a wide variety of mammalian cells, we tested the efficacy of InsP6 in growth reduction of K-562 human erythroleukemia cells in vitro. We report that InsP6 decreases the K-562 cell population by 19-36% (P less than 0.001) concomitant to an increased differentiation as evidenced by ultrastructural morphology and increased hemoglobin synthesis. Pilot experiments to study the mechanism of action of InsP6 show that following treatment with InsP6, the concentration of intracellular [Ca2+] ([Ca2+]i) is increased by 57% (P less than 0.02). Likewise, a 41% increase (P less than 0.05) in InsP3 and a 26% decrease (P less than 0.02) in InsP2 were noted 1 h following treatment with InsP6. Contrary to the dogma that cell division is associated with increased [Ca2+]i, our data show that reduced cell growth and enhanced differentiation is associated with increased [Ca2+]i and increased InsP3 in the presence of InsP6.

Long-term culture of normal human colonic epithelial cells in vitro

Studies of normal cellular function as well as the understanding of cellular mechanisms of carcinogenesis and other diseases of the large intestine have been limited, particularly due to the lack of long-term culture of normal human large intestinal epithelial cells (NHLIEC). Using the epithelia from surgically resected human colon, we have dissociated a sufficient number of viable NHLIEC and maintained them in in vitro culture for up to 5 months. Normal-appearing human large intestinal mucosal fragments (1 mm2) were treated with 0.01 mg/ml trypsin, 0.2 mg/ml collagenase + 0.1 mM EGTA or 0.1 mg/ml trypsin + 0.1 mM EGTA in a Stomacher laboratory blender to isolate the cells. Compared with other methods, the use of the Stomacher blender combined with low concentrations of proteolytic enzymes yielded greater numbers of cells per gram of tissue, with up to 84% viable cells. Primary and serially passaged NHLIEC were cultured in CMRL-1066, MEM with 5% serum, and serum-free KGM. These media were all supplemented with insulin, hydrocortisone, epithelial growth factor, and bovine pituitary extract. CMRL-1066 was found to be the best medium for NHLIEC. Contaminating fibroblasts were selectively removed by briefly allowing the cells to adhere to the culture vessel and adding 25 U/ml collagenase to the culture media at the first subculture treatment. The epithelial nature and secretory function of the established cells were confirmed by morphological criteria (light microscopy, phase contrast microscopy and electron microscopy), immunoreactivity to cytokeratin, and positive mucin cytochemistry. We propose that using this methodology for the culture and maintenance of NHLIEC for an extended period of time would serve as a valuable model for a variety of investigations.

Stability of fecapentaene-12 and its carcinogenicity in F-344 rats

Carcinogenicity studies of the fecal mutagen fecapentaene-12 (FP-12) have been hampered because of its apparent instability. We report here that: (i) contrary to the popular belief, FP-12 is quite stable, particularly at micromolar to nanomolar concentration; and (ii) its characteristic spectrophotometric absorbance spectrum is a function of the solvent or vehicle. Using synchronous fluorescence spectrophotometry (SFS), we have determined that at delta lambda 36.5 nm FP-12 gives a characteristic single emission peak between 413 and 423 nm, allowing us to identify FP-12 in DNA when reacted in vitro. We also report an increased incidence (statistically not significant) of fibrosarcomas and mammary carcinomas in male F-344 rats following intrarectal instillation of FP-12. In the in vitro human colon explant model, direct addition of FP-12 results in alteration in mucin histochemical changes typical of precancer and cancer. Our results support the contention that FP-12 is a naturally occurring carcinogen and may be responsible for human cancer(s).

Inositol-phosphate-induced enhancement of natural killer cell activity correlates with tumor suppression

In recent studies, we have demonstrated that inositol hexaphosphate (InsP6) inhibits experimental colon carcinogenesis. Since natural killer (NK) cells are involved in tumor cell destruction, we investigated the effect of InsP6 on murine NK cell activity. We show that; (i) 1,2-dimethylhydrazine (DMH), a colon carcinogen, depresses NK activity; (ii) in vivo treatment of mice with InsP6 enhances baseline NK activity and reverses DMH-induced depressed NK activity with an inverse correlation (r = -0.9811) with tumor incidence, (iii) short-term in vitro treatment of spleen cells and NK-enriched fraction with InsP6 also enhances NK cytotoxicity in a dose-dependent manner, (iv) inositol potentiates the action of InsP6. Our data suggest yet another important role of inositol phosphates in the regulation of cellular activity.

Phorbol ester-induced loss of membrane sialic acid: implications for tumor cytolysis by natural killer cells

Freeze-fracture analysis has shown that treatment of cells with phorbol myristate acetate (PMA) results in a loss of intramembranous particles (IMP) associated with the external leaflet of their plasma membranes. It has also been demonstrated that phorbol esters markedly enhance the sensitivity of tumor targets to natural killer (NK) cells, although the mechanism underlying this phenomenon has remained unexplained. Since the ability of NK cells to recognize neoplasms appears to be inversely related to the concentration of sialic acid on the target cell surface, it seemed possible that phorbols affect membrane glycoproteins which have terminal carbohydrates bearing sialic acid residues. To investigate whether phorbol treatment could be responsible for the loss of sialic acid, four tumor cell lines were examined before and after exposure to PMA. A reduction in surface sialic acid was established by four different methods: 1) standard thiobarbituric acid analysis of cell hydrolysates, 2) metabolic labelling of cells with [3H]-mannosamine followed by treatment with neuraminidase, 3) chromatography of membrane extracts, and 4) freeze-fracture analysis of lectin-labelled intact cells. These observations suggest a mechanism whereby phorbols may facilitate NK-cell-mediated cytolysis. In addition, an entirely novel effect of these tumor-producing agents may have been uncovered.