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I. Screpanti - Analysis of the role of preTCR-triggered NF-kB in T cell leukemogenesis
proliferation of lymphoma cells (Bellavia et al.,
EMBO J 2000, 19:3337). The analysis of Notch3-
IC/p52-/- double mutant mice showed that the
course of the T cell lymphomas was slightly delayed
and 80% of the mice were dead at 15 weeks of age
(vs 12 weeks of Notch3-IC single mutant animals).
However, at the end point the phenotype of the mice
was not significantly different from the Notch3-IC
transgenics: lethargy, hunched posture and distended
abdomen. At necroscopy the mice revealed a significant
enlargement of the upper mediastinum, and
increase in size and weight of spleen and lymph
nodes. Thus, as expected from the results previously
obtained, the inhibition of the alternative pathway of
NFkB activation, does not affect significantly the
development of the Notch3-induced T cell leukemia.
Preliminary experiments to study the immunophenotype
of lymphoid organs were done at the age of
7 weeks, when most of the Notch3-IC transgenic
mice display the characteristic features of Notch3induced
T cell leukemia (i.e. presence of CD4+CD8+
double positive cells in the spleen, increased expression
of CD25 and CD3 in both thymocytes and
splenic lymphocytes) and we did not observe significant
modifications in double mutant mice.
Interestingly, as a peculiar feature, the double mutant
mice displayed a virtual absence of B220+ cells
(0.5% vs 12% in Notch3-IC transgenic) and a significant
increase of Mac1+ (38% vs 4% in Notch3-IC
transgenic) and Gr1+ (30% vs 1% in Notch3-IC
transgenic) cells in the spleen.
b) Notch3-IC/p50-/- double mutant mice. We previously
described that the triggering of the canonical
pathway of NFkB activation, was mainly responsible
for the transcriptional activation of anti-apoptotic
and pro-proliferative genes, thus mainly responsible
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for the progression of T cell leukemia in Notch3-IC
transgenic mice. Since the canonical pathway activity
is sustained by the p50/p65 heterodimer, we would
expect that deletion of p50 would delay or even abolish
the development of T cell leukemia. Surprisingly,
the mortality curve showed that most of the mice die
earlier with respect to Notch3-IC single mutant mice.
Indeed 80% of the double mutant mice were dead at
8.5 weeks of age (vs 35% of Notch3-IC transgenic
and none of p50-/- mice) and all of the mice are dead
by 12 weeks of age. However, in any of the double
mutant mice we were able to detect the features of
leukemia/lymphoma. Rather, the mice appear significantly
smaller in size with respect to wild type or single
mutant mice of the same age and, while displaying
a spleen of normal size, their thymus was significantly
reduced, with a total thymocyte yield equivalent
to less than 10% of the cellularity of the thymus
from wild type or single mutant mice. Similarly to
what observed in Notch3-IC/p52-/- mice, also
Notch3-IC/p50-/- mice display a significant reduction
in the spleen of B220+ cells and a concomitant
increase of Mac1+ and Gr1+ cells.
Selected publications
Bellavia D, Mecarozzi M, Campese AF, Grazioli P,
Talora C, Frati L, Gulino A, Screpanti I. Notch3 and
the Notch3-upregulated RNA-binding protein HuD
regulate Ikaros alternative splicing. EMBO J. 2007,
26:1670-80.
Bellavia D, Checquolo S, Campese AF, Felli MP,
Gulino A, Screpanti I. Notch3: from subtle structural
differences to functional diversity. Oncogene
2008, 27:5092-8.