3. Aberrantly high and/or deregulated expression of
Myc is implicated in the majority of cancers
However, in most tumors, aberrant Myc
expression appears not to be due to
mutation in the c-Myc gene itself
6. Targeted allele in
TET-Myc mice
~10.1 kb
Not I
E1 E2 TRE E3 L2 Neo
Hind IIIR1
x
Targeting of the c-Myc Locus with a
Tetracycline Responsive Element (TRE)
c-Myc allele in
wild-type mouse
E1 E2 E3
Not I
~6.1 kb
R1 R1HindIII
TET-Myc repressor
targeting vector
E1 E2 TRE E3 L2 Neo HSV-TK
NotI
pBluescript
HindIII
x
Not I
7. Heterologous Repressor Targeting
Strategy of c-Myc Gene
c-Myc
c-MycTRE/TRE
TRE
tTSKid
Hybrid
Repressor
β-actin tTSKid
TS
KRAB
β-actin-tTSKid
Modified TET
transactivator
Transcriptional
repressor
c-Myc susceptible to
tetracycline-regulatable
repression
8. Heterologous Repressor Targeting
Strategy of c-Myc Gene
Presence of
Tetracycline
tTSkid
is inactivated, normal
expression of c-Myc
TET TS
KRAB
TET
E1 E2 TRE E3 L2 Neo
R1
x
HindIIINot I
Absence of
Tetracycline
c-Myc expression is blocked
by the super-repressor
tTSKid
Hybrid
Repressor
TET
Operator
Sequence
E1 E2 TRE E3 L2 Neo
R1
x
HindIIINot I
TS
KRAB
11. Growth Curve in c-MycTRE/TRE;
β-actin-
tTSKid MALFs
NumberofcellsX105
Days
+ Tetracycline
- Tetracycline
+ Tetracycline
12. Conclusions and Future Directions
• Myc inhibition represses cell proliferation
• Ability of reversibly inhibiting Myc at will
• Basic approach towards cancer therapy
• Method is to be tested in vivo
What is Myc? Myc is a transcriptional activator that regulates many intracellular and extracellular somatic cell programs, including proliferation (cell division), cell growth, cell cycle progression, metabolism, and apoptosis (death of cells).
Oncogenically overexpressed Myc is not the driving mutation in most tumors. Instead, deregulation of endogenous Myc in most cancers is due to persistent signals from upstream oncoproteins such as oncogenic kinases, Ras, or the Wnt/-catenin pathway. Endogenous Myc act as a downstream conduit for upstream oncogenic signals. What is the therapeutic potential of inhibiting Myc in vivo?
Here, we show that Myc is not the driving mutation in tumors. Instead, there are upstream cancer causing signals that lead to the overexpression and deregulation of Myc, underlying the fact that Myc serves as a conduit for such signals. Ultimately, endogenous Myc will lead to cancer. We now question whether inhibition of Myc expression in vivo can be a therapeutic potential for cancer.
This diagram models the heterologous repressor targeting strategy of the c-Myc gene. On the left, we have a normal mouse, whereas on the right, we have a mouse that has TRE (TET operator sequence) that makes c-Myc susceptible to tetracycline-regulatable repression.
In the first diagram, we have a part of the c-Myc allele in a wild-type mouse. Shown in the boxes labeled E1, E2, and E3 are the exons, and any space after that on the red line are the introns.
