LDL Receptor-related Protein 1B Research Articles

LDL Receptor-Related Protein 1B Polymorphisms Associated with Increased Risk of Lymph Node Metastasis in Oral Cancer Group with Diabetes Mellitus.

Oral cancer ranks fourth among malignancies among Taiwanese men and is the eighth most common cancer among men worldwide in terms of general diagnosis. The purpose of the current study was to investigate how low-density lipoprotein receptor-related protein 1B (LDL receptor related protein 1B; LRP1B) gene polymorphisms affect oral squamous cell carcinoma (OSCC) risk and progression in individuals with diabetes mellitus (DM). Three LRP1B single-nucleotide polymorphisms (SNPs), including rs10496915, rs431809, and rs6742944, were evaluated in 311 OSCC cases and 300 controls. Between the case and control groups, we found no evidence of a significant correlation between the risk of OSCC and any of the three specific SNPs. Nevertheless, in evaluating the clinicopathological criteria, individuals with DM who possess a minimum of one minor allele of rs10496915 (AC + CC; p = 0.046) were significantly associated with tumor size compared with those with homozygous major alleles (AA). Similarly, compared to genotypes homologous for the main allele (GG), rs6742944 genotypes (GA + AA; p = 0.010) were more likely to develop lymph node metastases. The tongue and the rs6742944 genotypes (GA + AA) exhibited higher rates of advanced clinical stages (p = 0.024) and lymph node metastases (p = 0.007) when compared to homozygous alleles (GG). LRP1B genetic polymorphisms appear to be prognostic and diagnostic markers for OSCC and DM, as well as contributing to genetic profiling research for personalized medicine.

NOTCH1 mutation associates with impaired immune response and decreased relapse-free survival in patients with resected T1-2N0 laryngeal cancer.

BackgroundPatients with early-stage laryngeal cancer, even stage T1-2N0, are at considerable risk of recurrence and death. The genetic and immunologic characteristics of recurrent laryngeal cancer remain unclear.MethodsA total of 52 T1-2N0 laryngeal cancer patients were enrolled. Of these, 42 tissue samples were performed by targeted DNA sequencing, and 21 cases were performed by NanoString immuno-oncology targeted RNA sequencing to identify the distinct molecular bases and immunologic features associated with relapse in patients with early laryngeal cancer, respectively.ResultsTo the best to our knowledge, we present for the first time an overview of the genomic mutation spectrum of early-stage laryngeal cancers. A total of 469 genomic alterations were detected in 211 distinct cancer-relevant genes, and the genes found to be mutated in more than five patients (>10%) included tumor protein p53 (TP53, 78.5%), FAT atypical cadherin 1 (FAT1, 26%), LDL receptor related protein 1B (LRP1B, 19%), cyclin dependent kinase inhibitor 2A (CDKN2A, 17%), tet methylcytosine dioxygenase 2 (TET2, 17%), notch receptor 1 (NOTCH1, 12%) and neuregulin 1 (NRG1, 12%). Recurrent laryngeal cancer demonstrated a higher tumor mutation burden (TMB), as well as higher LRP1B mutation and NOTCH1 mutation rates. Univariate and multivariate analyses revealed that high TMB (TMB-H) and NOTCH1 mutation are independent genetic factors that are significantly associated with shorter relapse-free survival (RFS). Simultaneously, the results of the transcriptome analysis presented recurrent tumors with NOTCH1 mutation displayed upregulation of the cell cycle pathway, along with decreased B cells score, T cells score, immune signature score and tumor-infiltrating lymphocytes (TILs) score. The Cancer Genome Atlas (TCGA)-laryngeal cancer dataset also revealed weakened immune response and impaired adhesion functions in NOTCH1-mutant patients.ConclusionsGenomic instability and impaired immune response are key features of the immunosurveillance escape and recurrence of early laryngeal cancer after surgery. These findings revealed immunophenotypic attenuation in recurrent tumors and provided valuable information for improving the management of these high-risk patients. Due to the small number of patients in this study, these differences need to be further validated in a larger cohort.

Sphingosine-1-phosphate, a novel TREM2 ligand, promotes microglial phagocytosis to protect against ischemic brain injury

The mechanism of sphingosine-1-phosphate (S1P)-mediated phagocytosis remains unknown. Here, we found that S1P or FTY720 (an analog of S1P) promoted microglial phagocytosis in stroke independent of S1PRs. First, we used computer simulation of molecular docking to predict that S1P might be a ligand for triggering receptor expressed on myeloid cells 2 (TREM2). Next, microscale thermophoresis (MST), surface plasmon resonance (SPR) and liquid chromatography–tandem mass spectrometry (LC–MS/MS) were performed to reveal that S1P was a novel TREM2 ligand. Then, we confirmed the pro-phagocytosis of S1P targeting in Trem2-Dap12 transfected CHO cells and TREM2 knockdown microglia. Point mutation analysis showed that D104 was the critical binding residue. Trem2−/− mice were used to demonstrate the role of S1P-induced phagocytosis targeting on TREM2 in protecting against ischemic brain injury. Finally, further studies revealed that apolipoprotein E (APOE) loaded with S1P was released by microglia and bound to apoptotic neurons via LDL receptor related protein 1B (LRP1B) and thereby induced microglia to phagocytose apoptotic neurons. Overall, the present work reveals for the first time that S1P acts as a novel endogenous ligand of TREM2 to effectively promote microglial phagocytosis. Our findings provide a new lead compound for developing immunomodulator targeting on TREM2.

Genetic alternations and immune characteristics in patients with small cell lung cancer

Genetic alternations and immune characteristics in patients with small cell lung cancer

Prognostic significance of LDL receptor-related protein 1B in patients with gastric cancer.

LDLR-related protein 1B (LRP1B) is believed to internalize ligands through receptor-mediated endocytosis. Previous epigenetic and genetic studies have indicated that impaired LRP1B mRNA expression might be related to gastric carcinogenesis. However, expression and prognostic significance of LRP1B protein remain to be elucidated. This study aimed to unravel the clinicopathological characteristics of LRP1B protein expression in gastric cancer. Immunohistochemical staining with antibodies specific to LRP1B peptide, which has an EXXXLL motif-containing region in the C-terminal flexible loop for intracellular sorting, was performed with 100 gastric cancer tissue specimens. Out of 100 tissue specimens, 45 exhibited cytoplasmic localization of LRP1B immunoreactivity. This cytoplasmic localization of LRP1B was significantly higher (P = 0.044) in intestinal-type gastric cancer (25 of 44) than in diffuse-type gastric cancer (20 of 56). Notably, cytoplasmic LRP1B immunoreactivity was significantly associated with low clinicopathological stage and favorable prognosis of patients with diffuse-type gastric cancer (P = 0.014), but nor with intestinal-type gastric cancer (P = 0.994). Multivalent analysis revealed that cytoplasmic LRP1B immunoreactivity had an independent favorable prognostic value in diffuse-type gastric cancer (P = 0.046; hazard ratio 3.058, 95% confidence interval 1.022-9.149). In contrast, no significant relation of cytoplasmic LRP1B immunoreactivity to patients' prognosis was found in intestinal-type gastric cancer. Double immunocytochemical staining demonstrated that cytoplasmic LRP1B was co-localized with RAB11FIP1, which constituted the endocytic recycling compartments in diffuse-type gastric cancer cells. The findings of this study indicated that impaired endocytosis of the cytoplasmic domain of LRP1B, resulting in insufficient ligand internalization, is related to poor prognosis of patients with diffuse-type gastric cancer.

Characterization of genomic alterations and the significance of PI3K/mTOR pathway mutations and tumor mutational burden in non‑small cell lung cancer.

Lung cancer is the most prevalent cancer worldwide and non‑small cell lung cancer (NSCLC) is the most common subtype and accounts for 75% of all lung cancer cases. Although programmed death‑1/programmed death‑ligand‑1 (PD‑1/PD‑L1) blockade has shown good results in the clinic, numerous NSCLC patients still fail to respond to this therapy. In the current study, formalin‑fixed, paraffin‑embedded tumor and matched blood samples from 1,984 Chinese NSCLS patients were collected for detection of genomic alterations including single nucleotide variations, short and long insertions/deletions, copy number variations and gene rearrangements. The most common mutated genes were tumor protein p53 (55.70%; 1,105/1,984), epidermal growth factor receptor (52.47%; 1,041/1,184), KRAS proto‑oncogene GTPase (13.36%, 265/1084), cyclin dependent kinase inhibitor2A (12.30%; 244/1,984), LDL receptor related protein1B (11.09%; 220/1,984) and telomerase reverse transcriptase (10.58%; 210/1,984). Tumor mutational burden was calculated and results revealed that it was associated with PI3K/mTOR pathway gene mutations, and patient's gender, age, smoking status, and tumor stage. In addition, mutations of phosphatidylinositol‑4,5‑bisphosphate 3‑kinase catalytic subunit α or F‑box and WD repeat domain containing 7 were detected in 3 patients with NSCLC who were resistant to PD‑1 inhibitors nivolumab and pembrolizumab. Disease stabilization and tumor shrinkage were observed in these patients after mTOR inhibitor everolimus treatment. The current data showed that NSCLC with PI3K/mTOR mutations are sensitive to mTOR inhibitors.

Abstract PD1-04: Nuclear localization of intracellular domain of LDL receptor-related protein 1B predicts poor outcome in breast cancer; putative relation to NEAT1 mediated mammary gland carcinogenesis

Abstract Background:Low-density lipoprotein receptor-related protein 1B(LRP1B) is thought to have a pleiotropic biological function. Notably, intracellular domain of LRP1B is released and transported to nucleus in a γ-secretase dependent fashion; however, pathological property, which is driven by nuclear transport of intracellular domain of LRP1B is largely unclear. In this study, we aimed to unravel the pathological significance of nuclear localization of intracellular domain of LRP1B in mammary gland carcinogenesis. Aims: We examine the clinical significance of LRP1B for breast cancer and we clarify mechanism of nuclear localization of LRP1B in invasive ductal carcinoma. Methods: Immunohistochemical staining using newly generated antibodies to intracellular domain of LRP1B was used to determine LRP1B expression in 92 invasive ductal carcinomas of the breast. The clinicopathological significance including prognosis value was statistically analyzed. Doxycycline dependent nuclear expression of intracellular domain of LAP1B was established in cultured breast cancer cells. Subsequently, a series of in vitro experiments were performed to explore the role of nuclear localized intracellular domain of LRP1B in cultured breast cancer cells. Comprehensive microarray-based analysis followed by quantitative RT-PCR and chromatin immunoprecipitation assay was performed to know the altered molecular signature induced by nuclear localized intracellular domain of LRP1B. Results: Non-tumorous mammary duct epithelial cells did not exhibit LRP1B staining, whereas different degrees of LRP1B immunoreactivity were observed in 75 of 92 invasive ductal carcinoma of the breast. LRP1B immunoreactivity was found in surface membrane and cytoplasm of 60 of 92(65.2%) invasive ductal carcinoma cells, whereas it was detected in nucleus of 15 of 92(16.3%)cancer cells. Interestingly, nuclear LRP1B immunoreactivity was significantly associated with poor prognosis of the patients, especially with luminal A type breast cancers. Notably, nuclear localized intracellular domain of LRP1B significantly related to status of nodal metastasis in luminal A type breast cancers. Enforced nuclear expression significantly increased Matrigel invasion activity in MCF-7 luminal A breast cancer cells without affecting cell growth. Notably, nuclear expression of intracellular domain of LRP1B decreased transcription of LRP1B. Comprehensive microarray-based analysis demonstrated that nuclear expression of intracellular domain of LRP1B significantly increased the expression of long non-coding RNA nuclear paraspeckle assembly transcript1(NEAT1), which facilitates breast cancer invasion with poor survival. Conclusions: Present findings indicated that nuclear localized intracellular domain of LTP1B promoted breast cancer progression with a poor prognostic value, possible through NEAT1 pathway. Nuclear transport of intracellular domain of LRP1B could be a therapeutic target for breast cancer patients. Citation Format: Asano Y, Futamura M, Takeuchi T, Yoshida K. Nuclear localization of intracellular domain of LDL receptor-related protein 1B predicts poor outcome in breast cancer; putative relation to NEAT1 mediated mammary gland carcinogenesis [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr PD1-04.

The genetic and epigenetic association of LDL Receptor Related Protein 1B (LRP1B) gene with childhood obesity

Low-density lipoprotein Receptor Related Protein 1B (LRP1B) is homologous to the gigantic lipoprotein receptor-related protein 1 that belongs to the family of Low-density lipoprotein receptors. Previous genetic association studies of the LRP1B gene have shown its genetic association with obesity. Through exome sequencing of the LRP1B gene from a childhood severe obesity cohort (n = 692), we found novel single nucleotide polymorphism (rs431809) in intron 4, which has been significantly correlated with both body mass index (BMI) and waist-hip-ratio (WHR). Three methylations of CpG sites (cg141441481, cg01852095 and cg141441470) in the same intron were also significantly correlated with BMI and WHR. All CpG methylations had bimodal patterns, and were dependent on rs431809 genotypes. The genetic influences of obesity on the LRP1B gene may be linked to the interplay of CpG methylations in the same intron. Heritability of SNP interacts with epigenetic crosstalk in LRP1B. Genetic and epigenetic crosstalk of LRP1B gene may be implicated in the prevention and therapeutic approach to childhood obesity.

Nuclear localization of LDL receptor-related protein 1B in mammary gland carcinogenesis.

LRP1B intracellular domain is released and transported to the nucleus; however, pathological consequences of this nuclear transport are largely unclear. We aimed to unravel the pathobiological significance of nuclear localization of LRP1B intracellular domain in mammary gland carcinogenesis. Immunohistochemical staining using antibodies for LRP1B intracellular domain was performed to determine LRP1B expression in 92 invasive ductal breast carcinomas. LRP1B immunoreactivity was detected in the surface membrane and cytoplasm of 60 of 92 invasive ductal carcinomas and in the nucleus of 15 of 92 carcinomas. Nuclear LRP1B was significantly associated with poor patient prognosis, particularly luminal A type breast cancer, where it was significantly related to nodal metastasis. Doxycycline-dependent nuclear expression of LRP1B intracellular domain was established in cultured breast cancer cells. Enforced nuclear expression significantly increased Matrigel invasion activity in MCF-7 and T47D luminal A breast cancer cells. Moreover, enforced nuclear expression of LRP1B intracellular domain facilitated MCF-7 cells growth in mammary fat pad of nude mice, which was supplemented with estrogen. Comprehensive microarray-based analysis demonstrated that nuclear expression of LRP1B intracellular domain significantly increased long non-coding RNA nuclear paraspeckle assembly transcript 1 (NEAT1) expression, which facilitates breast cancer invasion with poor prognosis. Nuclear-localized LRP1B intracellular domain promoted breast cancer progression with poor prognosis, possibly through the NEAT1 pathway. Nuclear transport of LRP1B intracellular domain could be a therapeutic target for breast cancer patients. KEY MESSAGES: Nuclear LRP1B was significantly associated with poor patient prognosis. Nuclear LRP1B increased Matrigel invasion activity of breast cancer cells. Nuclear expression of LRP1B intracellular domain increased NEAT1 expression.

Targeted Sequencing Analysis of Pulmonary Adenocarcinoma with Multiple Synchronous Ground-Glass/Lepidic Nodules

IntroductionLung adenocarcinoma (ADC) with synchronous ground-glass/lepidic (GG/L) nodules is considered a distinct disease entity in multiple synchronous lung cancers. Few studies have performed next-generation sequencing analysis of these synchronous sequential lesions, and genetic alterations of GG/L nodules must be further investigated. MethodsWe performed targeted sequencing in ADC with synchronous atypical adenomatous hyperplasia (AAH), ADC in situ, or minimally invasive ADC from 16 patients. Next-generation sequencing was performed by using a customized panel including 154 cancer-associated genes. ResultsMultiple synchronous lesions in the same patient showed different mutation profiles, and some shared identically mutated genes. In five patients harboring EGFR-mutant ADC, their synchronous GG/L nodules had EGFR mutation; however, none was observed in EGFR wild-type ADC. The average numbers of exonic mutations were 4.2, 5.4, 4.0, and 5.4 in AAH, ADC in situ, minimally invasive ADC, and ADC, respectively. In each lesion type, various mutations, including LDL receptor related protein 1B gene (LRP1B), KRAS, EGFR, and BRAF were observed in AAH, and EGFR mutations were the most frequently observed in ADC. In all, 80% of mutations with a variant allele frequency of 20% or higher, which contained driver gene mutations, were identified in ADC. Intratumoral heterogeneity of the genetic profile was found between the lepidic and invasive areas of ADC, but the driver gene mutations were similar. ConclusionsThis study suggests that ADC and synchronous GG/L nodules are genetically independent tumors. Intratumoral genetic heterogeneity of ADC was present, but driver gene mutations were homogeneously distributed. Driver gene mutations with a high variant allele frequency were identified in the invasive tumor. These findings support the relevance of molecular characterization of lung ADC and synchronous GG/L nodules.

Targeted sequencing reveals genetic variants associated with sensitivity of 79 human cancer xenografts to anticancer drugs.

Although there has been progress moving from a ‘one-size-fits-all’ cytotoxic approach to personalized molecular medicine, the majority of patients with cancer receive chemotherapy using cytotoxic anticancer drugs. The sequencing analysis of 409 genes associated with cancer was conducted in the present study using 59 DNA sequences extracted from human cancer xenografts implanted into nude mice, of which sensitivity to 9 cytotoxic anticancer drugs [5-fluorouracil, nimustine, adriamycin, cyclophosphamide, cisplatin, mitomycin C (MMC), methotrexate, vincristine (VCR), and vinblastine] was examined. The present study investigated the association between the sensitivities of the xenografts to the 9 anticancer drugs and the frequency of single nucleotide variants (SNV). The correlation between the expression level of the genes and sensitivities to the 9 drugs in the above xenografts was also estimated. In the screening study using 59 xenografts, 3 SNVs (rs1805321, rs62456182 in PMS1 Homolog 2, Mismatch Repair System Component and rs13382825 in LDL Receptor Related Protein 1B), were associated with sensitivity to VCR and MMC, respectively (P<0.001). A replication study of 596 SNVs was subsequently performed, which indicated P<0.05 in the screening study using independent samples of 20 xenografts. A combined result of the screening and replication studies indicated that 35 SNVs were potentially associated with sensitivities to one or more of the nine anticancer drugs (Pcombined=0.0011–0.035). Of the 35 SNVs, rs16903989 and rs201432181 in Leukemia Inhibitory Factor Receptor α and Adhesion G Protein-Coupled Receptor A2 were commonly associated with sensitivity to 2 or 4 anticancer drugs, respectively. These findings provide novel insights which may benefit the development of personalized anticancer therapy for patients with cancer in the future.

Abstract 136: Genetics of White Matter Hyperintensity Burden in Patients With Ischemic Stroke: The MRI-GENIE Study

Introduction: The MRI-Genetics Interface Exploration (MRI-GENIE) study is the first international collaboration that aims to facilitate genetic discoveries in clinical cohorts of patients with acute ischemic stroke (AIS). We have amassed the largest-to-date collection of AIS cases with brain MRI scans and genome-wide genotyping to test the role of genetic susceptibility in MRI-based cerebrovascular traits. Objective/Hypothesis: To elucidate the genetic architecture of white matter hyperintensity (WMH) burden in AIS patients. Methods: Using a novel automated algorithm, we extracted WMH volume (WMHv) from clinical MRI scans of 2704 AIS patients (age 63.1 ± 14.7 years, 60.6% male) of European ancestry. Quality control (QC) measures were undertaken per subject and per SNP, excluding subjects with non-European ancestry and poor genotyping, as well as SNPs deviating from Hardy-Weinberg equilibrium and high levels of missingness. Imputation to the Haplotype Reference Consortium (HRC version r1.1) was conducted for 1712 remaining subjects with 2.8 million SNPs on the Michigan Imputation Server. After exclusion of poorly imputed SNPs (R 2 &lt;0.5) and SNPs with minor allele frequency &lt; 1%, 7.7 million SNPs remained for further analysis. Genome-wide association testing of natural log-transformed WMHv on the allelic dosage per SNP was adjusted for age, sex and principal components 1-10. Results: Genome-wide association testing has identified a novel locus on chromosome 2 (T allele at rs72856504) near the LDL Receptor related Protein 1B gene (LRP1B) that was significantly associated with WMHv burden in AIS (β=0.54, SE=0.098, p=3.65*10 -8 ). Conclusion: We have identified a novel locus (T allele rs72856504) on chromosome 2 near the LRP1B gene, which is specific for WMH in AIS and has not been previosuly described in stroke-free WMH cohorts. A replication effort involving additional independent cohorts of AIS patients with brain MRI and genome-wide genotyping is ongoing.

Sleeping Beauty transposon mutagenesis identifies genes that cooperate with mutant Smad4 in gastric cancer development

Mutations in SMAD4 predispose to the development of gastrointestinal cancer, which is the third leading cause of cancer-related deaths. To identify genes driving gastric cancer (GC) development, we performed a Sleeping Beauty (SB) transposon mutagenesis screen in the stomach of Smad4(+/-) mutant mice. This screen identified 59 candidate GC trunk drivers and a much larger number of candidate GC progression genes. Strikingly, 22 SB-identified trunk drivers are known or candidate cancer genes, whereas four SB-identified trunk drivers, including PTEN, SMAD4, RNF43, and NF1, are known human GC trunk drivers. Similar to human GC, pathway analyses identified WNT, TGF-β, and PI3K-PTEN signaling, ubiquitin-mediated proteolysis, adherens junctions, and RNA degradation in addition to genes involved in chromatin modification and organization as highly deregulated pathways in GC. Comparative oncogenomic filtering of the complete list of SB-identified genes showed that they are highly enriched for genes mutated in human GC and identified many candidate human GC genes. Finally, by comparing our complete list of SB-identified genes against the list of mutated genes identified in five large-scale human GC sequencing studies, we identified LDL receptor-related protein 1B (LRP1B) as a previously unidentified human candidate GC tumor suppressor gene. In LRP1B, 129 mutations were found in 462 human GC samples sequenced, and LRP1B is one of the top 10 most deleted genes identified in a panel of 3,312 human cancers. SB mutagenesis has, thus, helped to catalog the cooperative molecular mechanisms driving SMAD4-induced GC growth and discover genes with potential clinical importance in human GC.

Identification of LRP1B-interacting proteins and inhibition of protein kinase Cα-phosphorylation of LRP1B by association with PICK1

Recent studies show LDL receptor-related protein 1B, LRP1B as a transducer of extracellular signals. Here, we identify six interacting partners of the LRP1B cytoplasmic region by yeast two-hybrid screen and confirmed their in vivo binding by immunoprecipitation. One of the partners, PICK1 recognizes the C-terminus of LRP1B and LRP1. The cytoplasmic domains of LRP1B are phosphorylated by PKCα about 100 times more efficiently than LRP1. Binding of PICK1 inhibits phosphorylation of LRP1B, but does not affect LRP1 phosphorylation.This study presents the possibility that LRP1B participates in signal transduction which PICK1 may regulate by inhibiting PKCα phosphorylation of LRP1B. Structured summaryMINT-6801075: Lrp1b (uniprotkb:Q9JI18) physically interacts (MI:0218) with SNTG2 (uniprotkb:Q925E0) by two hybrid (MI:0018)MINT-6801030, MINT-6801468: Lrp1b (uniprotkb:Q9JI18) physically interacts (MI:0218) with Pick1 (uniprotkb:Q80VC8) by two hybrid (MI:0018)MINT-6801284: LRP1B4 (uniprotkb:Q9JI18) physically interacts (MI:0218) with RanBPM (uniprotkb:P69566) by anti tag coimmunoprecipitation (MI:0007)MINT-6801108: Lrp1b (uniprotkb:Q9JI18) physically interacts (MI:0218) with Grb7 (uniprotkb:Q03160) by two hybrid (MI:0018)MINT-6801090: Lrp1b (uniprotkb:Q9JI18) physically interacts (MI:0218) with RanBPM (uniprotkb:P69566) by two hybrid (MI:0018)MINT-6801008: Lrp1b (uniprotkb:Q9JI18) physically interacts (MI:0218) with Jip-1b (uniprotkb:Q9WVI9-1) by two hybrid (MI:0018)MINT-6801052: Lrp1b (uniprotkb:Q9JI18) physically interacts (MI:0218) with Jip-2 (uniprotkb:Q9ERE9) by two hybrid (MI:0018)MINT-6801258, MINT-6801271: LRP1B4 (uniprotkb:Q9JI18) physically interacts (MI:0218) with Pick1 (uniprotkb:Q80VC8) by anti tag coimmunoprecipitation (MI:0007)MINT-6801244: RanBPM (uniprotkb:P69566) physically interacts (MI:0218) with mLRP4 (uniprotkb:Q8VI56) by anti tag coimmunoprecipitation (MI:0007)MINT-6801131, MINT-6801158: LRP1B4 (uniprotkb:Q9JI18) physically interacts (MI:0218) with Jip-1b (uniprotkb:Q9WVI9-1) by anti tag coimmunoprecipitation (MI:0007)MINT-6801231: PICK1 (uniprotkb:Q80VC8) physically interacts (MI:0218) with mLRP4 (uniprotkb:Q8VI56) by anti tag coimmunoprecipitation (MI:0007)MINT-6801173: Jip-1b (uniprotkb:Q9WVI9-1) physically interacts (MI:0218) with mLRP4 (uniprotkb:Q8VI56) by anti tag coimmunoprecipitation (MI:0007)

Slow endocytosis of the LDL receptor-related protein 1B: Implications for a novel cytoplasmic tail conformation

The LDL receptor-related protein 1B (LRP1B) is a putative tumor suppressor homologous to LRP1. Both LRP1 and LRP1B contain cytoplasmic tails with several potential endocytosis motifs. Although the positions of these endocytic motifs are similar in both receptors, LRP1B is internalized at a 15-fold slower rate than LRP1. To determine whether the slow endocytosis of LRP1B is due to the utilization of an endocytosis motif other than the YATL motif used by LRP1, we tested minireceptors with mutations in each of the five potential motifs in the LRP1B tail. Only mutation of both NPXY motifs together abolished LRP1B endocytosis, suggesting that LRP1B can use either of these motifs for internalization. LRP1B contains a unique insertion of 33 amino acids not present in LRP1 that could lead to altered recognition of trafficking motifs. Surprisingly, deletion of this insertion had no effect on the endocytosis rate of LRP1B. However, replacing either half of the LRP1B tail with the corresponding LRP1 sequence markedly accelerated LRP1B endocytosis. From these data, we propose that both halves of the LRP1B cytoplasmic tail contribute to a unique global conformation, which results in less efficient recognition by endocytic adaptors and a slow endocytosis rate.