Two novel human NUMB isoforms provide a potential link between development and cancer

Aldona Karaczyn,Chris Kubu,Douglas Spicer,Joseph M Verdi,Calvin Vary,Robert Friesel,Rebecca Cowling,Mahmud Bani-Yaghoub,Tamara L Adams,Roger Tremblay,Igor Prudovsky

doi:10.1186/1749-8104-5-31

Abstract

We previously identified four functionally distinct human NUMB isoforms. Here, we report the identification of two additional isoforms and propose a link between the expression of these isoforms and cancer. These novel isoforms, NUMB5 and NUMB6, lack exon 10 and are expressed in cells known for polarity and migratory behavior, such as human amniotic fluid cells, glioblastoma and metastatic tumor cells. RT-PCR and luciferase assays demonstrate that NUMB5 and NUMB6 are less antagonistic to NOTCH signaling than other NUMB isoforms. Immunocytochemistry analyses show that NUMB5 and NUMB6 interact and complex with CDC42, vimentin and the CDC42 regulator IQGAP1 (IQ (motif) GTPase activating protein 1). Furthermore, the ectopic expression of NUMB5 and NUMB6 induces the formation of lamellipodia (NUMB5) and filopodia (NUMB6) in a CDC42- and RAC1-dependent manner. These results are complemented by in vitro and in vivo studies, demonstrating that NUMB5 and NUMB6 alter the migratory behavior of cells. Together, these novel isoforms may play a role in further understanding the NUMB function in development and cancer.

Highlights

Numb was originally described as a mutation affecting the binary division of the sensory organ progenitor cells and a key player in neural cell fate decisions in Drosophila [1,2,3,4]
To detect transient NUMB expression, cells were examined in the undifferentiated state and at time points from 4 days to 5 weeks of retinoic acid treatment using human NUMB-specific primers that annealed just 5’ to the splice site contained within the phosphotyrosine binding (PTB) domain insertion site and 3’ to the splice site within the proline rich region (PRR) [6] (Additional file 1)
The cloning and sequencing of these products revealed an in-frame NUMB cDNA that had a 294-nucleotide deletion located between the PTB domain and PRR splice sites (Figure 1B)

Summary

Introduction

Numb was originally described as a mutation affecting the binary division of the sensory organ progenitor cells and a key player in neural cell fate decisions in Drosophila [1,2,3,4]. Loss of Numb function results in cells adopting non-neuronal fates, while ectopic Numb expression leads to additional neurons in Drosophila at the expense of other differentiated cell types. The cloning of mammalian Numb homologues [5,6,7] and the subsequent demonstration that these homologues affect mammalian differentiation outcomes [5,6,7,8,9] suggest an evolutionarily conserved function for Numb. These data are further supported by Numb knock-out phenotypes [10,11]. In addition to its role in neurogenesis, Numb has been considered

Methods

Results

Conclusion