# Functional Consequences of Ubiquitin Depletion During B Lymphocyte Differentiation

> **NIH NIH K08** · BRIGHAM AND WOMEN'S HOSPITAL · 2022 · $207,255

## Abstract

Project Summary/Abstract
Multiple myeloma (MM) is an incurable cancer of terminally differentiated plasma cells (PC),
characterized by abundant immunoglobulin (Ig) synthesis. Most PC are short lived and die only a few
days after differentiation through unclear molecular mechanisms. MM pathogenesis also remain elusive
with no single genetic driver mutation, but pervasive DNA damage. We have previously shown
increased cargo of polyubiquitinated (polyUb) proteins and decreased proteasome activity in
differentiating B lymphocytes and we hypothesized proteotoxicity as driver of PC death. By using
absolute mass spectrometry (AQUA) to quantify ubiquitin (Ub) in the same B cell differentiation model,
our preliminary data show that 60% free Ub depletion occurs in PC compared to resting B cells,
concomitantly with maximal Ig secretion and apoptosis. Second, we discovered that cells surviving long
term post differentiation can be identified and display markers of ongoing DNA damage. As Ub is
necessary for proper DNA damage response (DDR), polyUb protein degradation and DDR compete for
the same Ub pool. Based on our work, we propose a unifying model for short-lived PC death and MM
pathogenesis centered on critical Ub depletion. Our core hypothesis is that in PC, proteotoxic stress
secondary to sustained Ig synthesis, leads to free Ub depletion thus causing impaired DDR. Most PC
will be unable to recover from this crisis, however a small subset of genomically unstable PC may
survive, presumably due to accumulation of survival promoting mutations, constituting a premalignant
state for MM. We further hypothesize that Ub gene Ubc may be a haploinsufficient tumor suppressor
genes in B cell malignancies. Herein, the applicant, Dr. Giada Bianchi, presents a comprehensive plan
to test these hypotheses articulated in 2 specific aims: (1) to probe a causative link between Ig synthesis,
Ub depletion and apoptosis in PC; and (2) to evaluate whether Ub depletion is sufficient to cause
genomic instability in PC and drive MM pathogenesis. Data gathered during the course of our
investigation will provide novel data regarding the biology of normal and malignant PC and potentially
uncover a novel oncogenic mechanism - functional depletion of Ub - with applicability to other
malignancies and opportunity for innovative, molecularly targeted therapies. To this end, Dr. Bianchi
has carefully selected a mentoring committee and collaborators who are world-renowned experts in Ub,
MM, DDR, proteomics and B cell biology. Such team will provide knowledge, models and technologies
to render the testing of Dr. Bianchi’s hypotheses feasible within the proposed 5-year frame. The
applicant’s mentoring committee has furthermore designed a detailed career plan based on regular
meeting, attendance of workshops, classes and international meetings which will further accelerate the
trajectory of Dr. Bianchi to become an independent investigator in cancer biology in the next 5 years.

## Key facts

- **NIH application ID:** 10459410
- **Project number:** 5K08CA245100-03
- **Recipient organization:** BRIGHAM AND WOMEN'S HOSPITAL
- **Principal Investigator:** Giada Bianchi
- **Activity code:** K08 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $207,255
- **Award type:** 5
- **Project period:** 2020-08-13 → 2025-07-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10459410

## Citation

> US National Institutes of Health, RePORTER application 10459410, Functional Consequences of Ubiquitin Depletion During B Lymphocyte Differentiation (5K08CA245100-03). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10459410. Licensed CC0.

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